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The comparative histology of the esophagus and stomach of birds of different food habits Lazareff, Anne Eileen 1949

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THE COMPARATIVE HISTOLOGY OP THE ESOPHAGUS AND STOMACH OP BIRDS OF DIFFERENT FOOD HABITS - - by ~ Anne Eileen Lazareff A Thesis submitted in partial fulfilment of the requirements for the degree of MASTER OF ARTS In the Department of Z O O L O G Y The University of British Columbia Ap r i l , 1949 - i i i -ABSTRACT A histological investigation was carried out on the esophagus and stanaoh of the following birds: kingfisher (Msgaoeroyle aloyon oaurina). Balifornia murre(Uria aalgae oalifornioa), soreeoh owl (Otus  asio kennioottiJ^Peale's faloon (Faloo perigrinius pealei). and sparrow hawk (Faloo sparverius sparverius)* A number of stains T S « 0 S used to intensify the different structures present. In the kingfisher, murre and owl the esophagus was a thin walled highly expansible tube of generally even calibre, whereas in the Peak's faloon the anterior part was dilated into orsao*" The wall of the esophagys possessed the usual struoture characteristic of this region of the digestive tube* Three types of glands have been distinguished i n these birds. In the kingfisher and owl simple oval glands were situated almost entirely within the epithelium. The glands and excretory duct were composed of similar c e l l s with slight variations ooouring in excre-tory duot lengths. In the California murre the glands were s t i l l simple but had sunken to the tunica propria with just the excretory duots passing through the epithelium. The gland oells were narrower, and the duct c e l l s resembled those observed in the owl and the kingfisher. These glands were a l l apocrine secretory. However, in the Peale*s faloorjand sparrow hawk secretion was holocrine. These glands were deeply embedded within the tunica propria and resembled the esophageal glands of the chicken. The excretory duotsirere lined by squamous epithial c e l l s * Although the birds examined possessed a variety of food habits* f i s h , mammals, birds and crustaceans) the food was essentially meat. However, - I V considerable variations in the structure of the esophagus were observed* The proventrioulus was comprised oft a mucosa, indented with minute gastric pits* a musoularis externa of three layers of smooth muscle, and a lamina adventitia that surrounded the entire tube* Within the mucosa the deep glands were situated. These were oomposed of large lobes,Aenveloped in a dense capsule of connective tissue and internally oonsisted of simple tubules that radiated about a oentral excretory duct* The structure of the proventrioulus was more or less uniform in the birds investigated, with only slight variations ooouring in cellular arrangement and cellular size* The gizzards in the birds examined were large spherical structures that f i l l e d a majority of the abdominal oavity* In the kingfisher, owl, Peale's falcon, and sparrow hawk, thee gizzard was lined by a thin keratinoid lining that was secreted by the glands present in the gizzard mucosa* The musoularis externa was of approximately equal thiokness throughout* In the murre, the keratinoid layer was five or six times as thiok as in the above birds and the muscles showed a heavy development on the dorsal and ventral sides* This development took plaoe toward a grinding mechanism that mis necessary for processing the hard shelled orustaoeans eaten by this bird* TABLE OP CONTENTS Table of Contents— — - — — — — — — — — i . A b s t r a o t - — — — — — — — — - — — - — — - — — i i L Introduction— — - — — — — — — iv. Acknowledgement s«*»»» — — — — — — — — — — — v i . Historical R e v i e w — — — — — — — — — — - I , Materials and Methods — — — — O b s e r v a t i o n s — — — — — — — — — — — — — 1 2 Esophagus Kingfisher (jfegaoeroyle aloyon oaurina)—-12. California murre(Uria aalgae c a l i f o r n l o a } — *5-Soreech owl (Otus aslo k e n n l o o t t l ) — — » — f Short-eared owl (Aslo flammeus flammeus)— — Peale's falcon (Palop perigrinius p e a l e i ) — Sparrow hawk (Faloo sparverius sparverius)— Pigeon hawk (Faloo oolumbarius sucklgyi) Proventrioulus Kingfisher (jfegaoeroyle aloyon o a u r i n a ) — » 2 2. California murre (Uria aalgae californioa)-- 24. Soreeoh owl(jQ±us asio k e n n i o o t t i ) - — — — — 25. Short-eared owl(Asio flammeus flammeus) Peale's faloon(Faloo per&grinus p a & l f l i ) — — 27. - i i -Sparrow hawk(Faloo sparverius sparverius) Pigeon hawk (Faloo oolumbarius suokleyi) Gizzard Kingfisher (Megaoeroyle aloyon oaurina^——»2Q^ California murre (Uria aalgae o a l i f o r n i o a ) - 3 l K Soreeoh owl (Otus asio kenniootti) — — — — 32. Peale's faloon (Faloo pertgrinius pealei)-- "3 4.. Sparrow hawk (Faloo sparverius sparverius) Pigeon hawk (Faloo oolumbarius suokleyi) Conolusions and S u m m a r y — — — — — — — — — — — Literature C i t e d — — 4f. P l a t e s — — • — 4 7 INTRODUCTION Although aotive investigations of the alimentary tract in birds have been carried out for nearly two oenturies our knowledge of this organ system s t i l l remains inadequate. The work of such men as Reaumur (1752) who concerned himself with the triturant action of the gizzard on introduced substances, Hunter (1786) who studied muscle move-ment and noises of stones in the gizzard, Cuvier (1805), Home (1814) and H. Milne Edwards (1857-1881) illustrates the early beginnings of Inquiry into the mechanisms of the digestive tract. It was not u n t i l the work of Molin (1853) that the f i r s t methods of histological teohnique were introduced and investigations turned more to the finer structures of the organs. Among the earlier workers who engaged themselves i n microana— tomical investigations were Berlin (1852), Leydig (1857), Flower (i860), Bergmann (1862), Hasse (1865),~ Curshman (1866), Wledersheim (1871), Gar-rod (1872) and Klein (1881). Even with their imperfect methods these men have made some advances to which only further knowledge can be added by continuous investigation and refinement i n apparatus and technique. It is the authorfa intention, in the study here presented, to add to accumulating knowledge concerning the alimentary tract of the birds. For this investigation, two groups of birds have been ohosenj one ohiefly a piscivorus group and the other a carnivorous one. To rep-resent the fish-eaters the western belted kingfisher (Megacerovle alcyon oaurina Grinnell) and the California murre (Uria aalgae. californica Bryant) were studied. The kingfisher is almost entirely a fish-eater while the California murre can exist equally well on f i s h or crustaceans -vt-(Taverner 1947). Of the carnivorous species chosen, the screech owl (Otus  asio kennicotti E l l i o t ) and the short-eared owl (Asio flammeus flammeus Pontoppidan) show preference for a diet consisting mainly of small mam-mals, while the Peale*s falcon (Faloo peregrinius pealei Ridgeway) and the black pigeon hawk (Faloo columbarius suckleyi Ridgeway) are examples of the few birds that prefer birds as food. (Taverner 1947, May 1935, Barcus 1930)8 The sparrow hawk (Balco sparverius aparverius Ridgeway) although i t belongs to the same genus as the Peale's falcon and pigeon hawk subsists contrary to the implications of i t s name, chiefly on i n -sects and only occasionally oaptures a bird (Taverner 1947, May 1935). In presenting this work, a comparative description w i l l be given f i r s t of the anatomy and histology of the esophagus and stomaoh of each speoies followed by an attempt to correlate the histological structure of the tract with the food habits of that species. - v i i -ACKNOWLED GEMENTS The writer i s indebted to Dr. W. A. Clemens and the members of the s t a f f of the Department of Zoology, University of B r i t i s h Columbia for granting permission to carry out t h i s investigation, especially to Professor G. J . Spencer for suggesting the problem and to Dr. I. MoT. Cowan for the kindly interest that he has shown. The author wishes to express her sincere appreciation f o r the helpful o r i t i o i s m and suggestions that Dr. J. A.CNicol has given i n the preparation of t h i s paper. Grateful appreciation i s extended tot Dr. I . MoT. Cowan, Dr. and Mrs. E. Black, Mr. F. L. Beebe, Mr. C. Guiget, Mr. P. Martin, Mr. C. Law and Mr. E. Samann for the c o l l e c t i o n of material used i n t h i s work; to Miss Anne M. Smith for obtaining many i n t e r l i b r a r y loans); to Miss Joan Hannay for typing t h i s t h e s i s j to Mr. R» S»teiner for his help i n photomicrogrophyj and f i n a l l y to Miss Vivian V e r r a l l , to my s i s t e r , E l s i e and to my fellow students for t h e i r co-operation at a l l times. THE COMPARATIVE HISTOLOGY OF THE ESOPHAGUS AND STOMACH OF BIRDS OF DIFFERENT FOOD HABITS HISTORICAL REVIEW Several authors have described b r i e f l y the general anatomy of the esophagus and stomaoh of birds, but very few have touched upon the histology of these regions other than those of the domestio fowl. Kingsley ( 1926) and Scheer (1948) i n describing the anatomy, of the digestive t r a c t of the bird spoke of the esophagus as an elon-gated tube with complex diverticulae. Kingsley( 1926) stated that i t was usual for the esophagus to be of uniform diameter but frequently i n birds marked d i l i t a t i o n s were present. Wiedersheim and Parker ( 1907) expressed the opinion that modifications of the esophagus occurred as adaptations a r i s i n g from food habits, the mode of l i f e and the absence of teeth i n birds. These workers found that i n gramnivorous birds and i n birds of prey either the whole gullet formed an expanded sac or a ventral outgrowth was present. This d i l a t a t i o n or outgrowth they referred to as the crop or ingluvies. Beddard (1898) stated that gallenacious birds were provided with a crop while other birds possessed a slight,permanent or temporary d i l a t a t i o n that forshadowed the f u l l y developed orop. Of the l i t e r a t u r e pertaining to the histology of the avian esophagus and crop, the majority deals with the domestic fowl. Very l i t t l e has been written about the histology of these structures i n other birds. Barthels (1895) desoribed b r i e f l y the histology of the - 2 -v©d£=%he esophagus of a number of birds, among which he mentioned --Uria lean via ( a murre) and fltus brachyotus ( the barn owl). Kaden ( 1932) on the other hand confined her work to a study of only the epithelium, glands and modes of secretion of these glands for a large group of birds. For the murre ( Uria lorn via) Barthels ( 1895) stated that - the esophagus was thrown into about twelve folds which disappeared at the proventrioulus. The epithelium was thick and consisted of small c e l l s . The glands were small with long sharp Hacks extending through the epithelium. The muscle layer consisted of an external cir o u l a r muscle .twSefcitaes as thick as the internal longtitudinal muscle layer. Both of the above mentioned authors have worked on various species of the Family Strigidae ( the owls). The esophageal w a l l of Gtus brachyotus ( the barn owl) was described by Barthels ( 1895) as highly folded and possessing a weakly developed mucosa. The e p i t h e l i a l c e l l was f i l l e d by a globular and s l i g h t l y flattened nucleus. Kaden (1932) i n d i s -cussing the epithelium of Asio otus stated that i t oonsisted of f l a t " o e lls with oval nu c l e i . The epithelium was thin and did not vary i n thickness throughout the whole length of the esophagus. Barthels described the esophageal glands as oval structures lined with cuboidal e p i t h e l -ium and possessing short excretory ducts. Kaden stated that these glands were round or oval with their form and size remaining the same throughout the esophagus. The gland c e l l secretion was transparent and granular and stained with muci-carmine. The glands excreted d i r e c t l y into the lumen. Borthels ( 1895) stated that the la&ina propria was made up of fibrous connective tissue with numerous round n u c l e i . Kaden (1932) said that i t hardly existed. The musoularis externa was described by Barthels (1895) as a f a i n t l y homogeneous layer consisting of an inner longtitudinal and a very w e l l developed outer o i r c u l a r musole layer. Many blood vessels were persent i n the adventitia. Kaden (1936) also described the structure of the epithelium and glands found i n Faloo tinnuncuius ( the tower falcon) The epitheliuoa in this species was cornified and possessed a t y p i c a l stratum lucidum i n the region of the crop. The c e l l s were large and very clear with round nu c l e i . The stratum lucidum disappeared gradually i n the thoracic region but remained i n the sinuses of the folds while the remaining epitheluim showed strong continuous f l a t t e n i n g . Complicated folded holocrine glands were present i n this species. The folds were narrow and the c y l i n d r i c a l epitheluim of the gland was so high that the lumen of the gland consisted only of thin branching tubes. The c e l l s of the exoretory ducts were f l a t squamous c e l l s resembling the e p i t h i l i a l c e l l s . The stomach i s divided i n t e r n a l l y into two regions. The an-t e r i o r part Cazin (1886V.) Beddard (1898) Wiedershfeim and Parker (1907) and Kingsley (1926) called the proventricuius because of i t s glandular development and the posterior, the muscular gizzard. Scheer (1948) on the other hand referred to the anterior section as the musuclar gizzard and the posterior as the proventriculus. Cazin (1886) found i n a number of birds of prey and i n certain f i s h eaters that the proventriculus showed great development, i t s walls were extensible and i t s volume exceeded that of the gizzard. .Often there was no d i v i s i o n between the glandular portion and that of the gizzard. In the hawk the stomaoh consisted of a pocket which dilat e d at the i n f e r i o r terminal portion into what Cazin called a "cul-de-sac". Beddard (1898) also found that the proventriculus was not always separated from the gizzard. In 1887 -4-Cazin made a study of the histology of the stomach of some birds and for water birds and for birds of prey ( s i c ) he described the proventrioulus as a glandular area with each compound gland formed by an agglomeration of tubules i n a bl i n d sac of connective tissue. Each gland possessed two types of c e l l s that never mixed within a single tube. The granular enzyme c e l l s were always l o c a l i z e d i n the tubules at the periphery of the gland while the mucous c e l l s existed i n the oentral cavity and i n the c o l l e c t i n g canals that received the products of seoretion of the enzymatio c e l l s . Bergmann (1862) distinguished between three types of proventricular glands. The f i r s t he described as those i n which the gland tubes opened d i r e c t l y into a central oavity; the seoond i n which the gland tubules entered a central cavity byway of secondary canals and a t h i r d , i n which a number of l i t t l e canals opened into the oavity of the stomaoh, one beside the other. In 1888 Cazin described the mucosa of the proventrioulus as consisting of f i n e outpushings, separated by deep ridges formed by the f o l d i n g of the mucosa . Generally these folds were continuations of the esophageal furrows that passed to the gizzard. Wiedersheim and Parker JC1907) stated that the glandular stomach alone took part i n dissolving the food and Scheer (1948) compared the proventrioulus to the stomach of other vertebrates. The second part of the stomach, the gizzard has attracted investigators for a long time. Indeed,as far back as 1752 observations have been carried out on the gizzard. A l l authors agreed that the gizzard had a mechanical function. Wiedershe<im and Parker(l907) stated I - 5 -that i n correlation with t h i s mechanical role a very peculiar and thick muscular w a l l provided with tendinous discs was developed. Kingsley (1926) said that the muscles of the gizzard w a l l were developed into two discs withtendinous centres. Cazin (1886b) did not observe tendin-ous areas i n the gizzards of raptores and f i s h eaters. In these birds he found that the muscular w a l l was much reduoed and had the same diameter throughout. Beddard (1898) also found that the gizzard was more muscular i n grain than i n flesh-and fish-eating birds. The degree of gizzard development according to Wiedersheim and Parker (1907) was i n d i r e c t proportion to the consistency of the food. Gadow (1879) also indicated b r i e f l y the musuolar grinding power of the gizzard i n a number of birds. Grain eaters he found possessed the thickest keratinoid l i n i n g and strongest muscular" w a l l while i n the birds of prey modification was least marked. The histology of the gizzard has been described by a few workers for several kinds of birds. Wiedersheim ( 1872) was the f i r s t observer who described the r e l a t i o n e x i s t i n g between the epitheluim of the glands of the gizzard and the secretion contained i n the i n t e r i o r of these glands. He showed that the p a r a l l e l s t r i a t i o n s observed i n cross sections of the muoosa were i n direct r e l a t i o n with the parietal; c e l l s of the glandular tube. These s t r i a t i o n s represented l i t t l e currents of secretions from the gland c e l l s . Cazin i n 1887 described generally the mucosa of the gizzard of f l e s h eating birds as consisting of tubular glands. These glands secreted the oornified covering of the gizzard. The covering he found to be a th i n soft membrane that could not be detached i n the form of a d i s t i n c t sheet as the horny-lining of the gizzard of grain-eating birds. Bauer (1901) confined his work c h i e f l y to the duck where his aim was to establish more exactly the r e l a t i o n of secretedy f i b r e s that form the gizzard l i n i n g «to the gland c e l l s . In agreement with Hedinuis Bauer (1901) proposed that the various p a r t i a l l y misleading terms l i k e horny layer, outicular layer and c u t l c u l a , used f o r the gizzard l i n i n g be surrendered i n favour of a more precise expression and be referredto as a "keratinoid" layer. SPECIMEN COLLECTING AREA Kingfisher 1 Kingfisher 2 California Murre 1 California Murre 2 California Murre 3 Screech Owl 1 Screech Owl 2 Short-eared owl "Screech Owl 3 Peale's Falcon 1 Pealed Falcon 2 Peale's Falcon 3 Sparrow Hawk Pigeon Hawk . Cowlchan Lake Cowichan Lake Wreck Beach Goose Island Goose Island Lulu Island Stanley Park Lulu Island Marine Drive Iangara Island Langara Island Goose Island Williams Lake Williams Lake. ESOPHAGUS total length ER07ENTRI CUIUS to t a l length GIZZARD length FIXATIVE 7.3 cms 1*2 8*0 2.0 NO M E A S U R E M E N T S 10.5 2.2 12.6 2.8 Incomplete 1.7 8.7 1.9 NO M E A S U R E M E N T S Incomplete 11.3 11.0 10.7 Incomplete Incomplete 1.5 2.6 2.7 2.8 1.7 3.5 cms 2.3 cms Bouin;: 2.5 Bouin Bouin 4.4 Bouin 4.9 Bouin 3.6 Bouin 3.5 Bouin Helly/s 2.5 Bouin 4.7 B.C.Fixative 4.3 B.C.Fixative 4.6 Bouin 2.7 Bouin 3.0 Bouin MATERIALS AND METHODS For' t h i s work the following materials? two kingfishers, three C a l i f o r n i a murres, three screeoh owls, a short-eared owl, three -fieale's falcons, one sparrow hawk, and one black pigeon hawk were supplied by f i e l d workers from various parts of B r i t i s h Columbia. In a l l but three instances, i n which case two owls and one murre were obtained a l i v e , material was supplied i n the fixed condition. Immediately following death, the bi r d was dissected and the entire eso-phagus and stomach were removed and placed into the f i x i n g eolution. An attempt was made to begin f i x a t i o n of the material before the heart ceased beating. Two incisions at the regions of the proventriculussand gizzard served to allow the f i x a t i v e to enter the i n t e r i o r more rapidly. In t h i s condition specimens remained u n t i l such time as they could conveniently be shipped. Fixative sjhad to be picked that were easy to use, that acted rapidly, and i n which materials oould remain for extended periods of time without deleterious effects. B.C. f i x a t i v e and Bouins' f l u i d were chosen. The proportions of ingredients for B.C. f i x a t i v e were f i r s t worked out by Dr. A..H.Hutchi-son of the University of B r i t i s h Columbia. In the preparation of t h i s f l u i d , he held i n mind two things -(1) To -obtain a good general fixative o.ndL. (2) to develop a solution that could be used to greatest advantage i n the f i e l d . Thus he obtained a solution that f i x e d r a p i d l y and one i n whioh tissue oould remain without destruction for periods of time up to three years or more. The proportions of materials for this f l u i d were as follows: Methanol 95% 250 co Glaoial acetio 5 co Formaldehyde 12 co Water 50 cc This solution was primarily intended for plant histology, but with a s l i g h t modification of thes formula,Professor G.J.Spencer was able to obtain a solution more suitable for animal c e l l s . He modified the formula as follows -Methanol ' 280 cc Glacial acetic 6 cc Formaldehyde 12 cc Water 100 co Although the above solution gave satisfactory r e s u l t s , Bouin'a f l u i d gave a better over-all f i x a t i o n . Of the three l i v i n g specimens obtained, the C a l i f o r n i a murre and one owl were gassed and f i x e d i n BouinS*- The other owl was k i l l e d by asphyxiation. The foregut was removed and preserved i n Holly's f l u i d , then post-chromed i n a saturated solution of potassium diohromate at 37°C for 48 hours i n an attempt to preserve the mitochondria. For comparison small sections of tissues were removed from the f i x a t i v e and treated for embedding. The material preserved i n B.C. f i x a t i v e was transferred for two or three days to dioxane, three changes; two changes of toluene, $ne and one half to two hours each; f..\.' .iircs -9- • Lc^ 'and three changes of tissue mat /(55 C to 56°C) for one hour to one and one half hours depending on ti(e size of the t i s s u e . Material f i x e d i n Bouin's solution was washed f i r s t i n 50 percent, alcohol, then placed i n 70 percent, with added l i t h u i m carbonate u n t i l most of the p i c r i c acid was removed. Prom 70 peroent alcohol i t was transferred either into dioxane and the procedure followed as above; or i t was dehydrated to 95 percent alcohol 2 changes; DBfore clearing i n toluene;" or taken to absolute alcohol and cleared i n cedar o i l . If the seotions were small enough, the cedar could be removed r e a d i l y , thus i n y ielding an e a s i l y cutting tissue. HQwever/the majority of the sections u s e d , d i f f i c u l t y was encountered with this method in removing the clearing agent during i n f i l t r a t i o n with wax. Pinal washing of the tissue i n toluene prior to emersing i n wax had l i t t l e e ffect i n removing the cedar o i l from some sections unless the washing was greatly prolonged. For embed-ding two waxes were employed. Ordinary p a r a f f i n was used i n the prelim-inary work; tissue mat (55° to 56°c) was used for the majority of the preparations. Best results were obtained by dehydrating i n dioxane, toluene and decreasing to a minimum the times of exposure of the tissues to heat. The gizzards even with the above precautions could not be sectioned without further treatment. The keratinoid l i n i n g s tended to crumble at the touch of the k n i f e . Placing the gizzard blooks i n a s o f t -ening solution, consisting of a n i l i n e o i l one part and glycerine nine parts, (Lendrum ,(1944) prevented excessive crumbling and enabled^the'seotions to be cut. - 10-The material was sectioned at„four to twelve microns. The slides were cleaned f i r s t with acid then with pure alcohol. The sections were flattened on a water bath, then affi x e d to a s l i d e or warmed on a drop of water or 30 percent alcohol ( L i l l i e 1948) d i r e o t l y on the slide on a metal sheet. A selection of stains was made with the purpose i n mind to in t e n s i f y p a r t i c u l a r structures. Ehrlich's and Harris' haematoxylin and eosini were used as general stains. To stain mucin Mayers muci-carmine anil BtMSaJf (Bensely A1938) was employed after haematoxylin. Methylene blue and eosin ( Galigher 1934) were also t r i e d for staining mUCUS . Somz d i f — ficulty^experienced with this technique v,vs i n determining a satisfactory sohedule of staining times that would y i e l d w e l l d i f f e r e n t i a t e d r e s u l t s . Heidenhain's agan-( Pantin 1046-)- and Mallory's t r i p l e stain ( Pantin 1946) were also employed as general stains. Azan gave a.n.cst b r i l l i a n t stain for connective tissue, reticulum, nerve ganglia and f i b r e s , yet clear contrast between nuclei and oytoplasm i n the smooth muscle could not be obtained. Mallory's t r i p l e gave excellent contrast but the method could not be r e l i e d upon since i t created a d i f f e r e n t effect i n each sl i d e although i t was surprisingly uniform i n staining nerves. Mallory's phosphotungstic acid haemotoxylin ( Bensley & Bensley 1938) produced fine d i f f e r e n t i a t i o n and very clear contrast between cytoplasm and n u c l e i . This stain was capable of d i f f e r e n t i a t i n g oollagenio tissue, 'elastio f i b r e s , f i b r o g l i a , myoglia, mi t o t i c figures and bringing out with clearness c e l l u l a r outlines. Several e l a s t i o tissue stains were used with good r e s u l t s . Van Gieson's stain showed white connective tissue and muscle w e l l . I t also stained nuolei and nuclear elements sharply. -11-The method used was as follows t (a) Stain sections deeply with haematoxylin ( one to two hours) (b) Rinse i n tap water. (c) Stain i n Van Gieson(ten cc of one percent aqueous solu-tion of acid fuchsin to 100 cc of saturated aqueous solution of p i c r i c acid) one to three minutes and when pale wash b r i e f l y i n water one-half second. (d) Transfer to 95 percent alcohol followed by absolute alcohol. (e) Clear i n toluene and mount i n balsam. To bring out e l a s t i c tissue orcein ( Bensley & Bensley 1938) and Verhoeff's ( Galigher 1934) e l a s t i c tissue stains were t r i e d , (Drcein gave a very f a i n t stain generally except where dense e l a s t i c tissue was present. Verhoeff's was not as delicate i n staining dense e l a s t i c tissue but i t brought out f a i n t e l a s t i c f i b r e s that were completely missed by orcein. As a counter s t a i n Van Gieson was substituted f o r eosin i n some cases. For r e t i c u l a r f i b r e s Foot's short method for s i l v e r impreg-nation of reticulum ( Bensley & Bensley 1938) was employed with Mallory's t r i p l e and Van Gieson as counterstains. Bodian's s i l v e r method for nerves ( Bodian 1936)was excellent. Mallory's t r i p l e counterstain gave good contrast and seemed to i n t e n s i f y the nerve f i b r e s and ganglia;;. Altmann's mitochondrial stain ( Bensley and Bensley 1938) was not successful. -12-OBERSERVATIONS Esophagus -Kingfisher ( Megaoeroyle aloyon oaurina) The esophagus of the Kingfisher oommunioates anteriorly with the pharynx and passes posteriorly between the bronchi to j o i n the pro-ventriculus. The tube l i e s dorsal to the traohea and is held loosely by connective tissue to the surrounding area (Plate I, f i g . 1). The esophageal wall is thrown into sixteen or eighteen longi-tudinal folds. At i t s base lateral folds are imposed upon the longitudi-nal ones, thus oreating a rig-ragging appearance of the wall ridges* The esophagus is generally oapable of great distension, but at this regi» on i t s e l a s t i c i t y is further increased so that i n addition a bulbous or crop-like dilation i s also possible (Plate III, fig*3Lb). Primarily three ooats constitute the structure of the wall, a muooaa consisting of a strat i f i e d epithelium and a lamina propria} -a musoularis externa with an inner longitudinal and an outer circular . layer) and f i n a l l y a tunioa adventitia* A musoularis muoosa is lacking and a submucosa oould not be differentiated from the tunica propria (Plate IV, fig.9)* The s t r a t i f i e d epithelium is comparatively thiok and extends eight or ten c e l l layers* In the germinative layer nearest the lamina propria the cells are polyhedral i n shape with their large oval nuclei arranged prependioularly to the lumen. In these c e l l s mitosis is frequently observed* la the middle layer nuolei and oells beoome nearly sperioal* The tipper or surfaoe layer shows the oells elongated and nuolei parallel to the lumen* At various points on the free surfaoe the oells may be seen passing through the preliminary stages of degeneration* The nuolei beoome pyknotio, the oells show large vacuoles* die and even-tually 8lough off* No oornifioation can be observed* Within the epithelium and just extending to the lamina are the esophageal glands* These are simple oval shaped structures arranged side by side throughout the entire esophagus (Plate 17, fig * 10 d). There is no apparent difference between the basal gland oells and those lining the excretory duct (Plate V, fi g * lla,b,)* A similar effect is obtained for a l l the oells when stained with muoi-oarmine* Sohaffer ( 1924) made a detailed study of the morphelogioal characteristics of digestive glands in mammals, and he developed a olas*— Jsifioation of the glands aooording to their struoture* He distinguished between a homoorine gland, that i s , one in which the secretory tubules are lined with oells of one type, and a heterocrine gland, one in whioh the secretory tubules are lined with oells of different types* He further divided the glands aooording to the number of layers present in the secretory epithelium as monoptyohial, i f the secretory epithelium is in one layer, and polyptychial i f more than one layer is present* On the basis of this classification the esophageal glands of the Kingfisher may be oalled homoorine monoptyohial glands* The gland oells are large cuboidal with spherical nuolei -which at secretion beoome closely pressed to the distal wall, while the oytoplasm f i l l s with granules (Plate V* fig* l i d ) . Upon secretion the - f 4 -apioal parts break down and liberate the granules* Regeneration of the oells and granules begins onoe again* Beneath the epithelium is a large lamina propria composed of dense oollagen with many compressed fibroblasts (Plate VI, f i g * 12 h)* At i t s junotion with the epithelium a retioular membrane or a group of reticular fibres surrounds the basal parts of the glands and passes across the peaks of the lamina papillae that extend between the glands* Under high power faint elastic fibres oan be observed throughout the lamina* Small arteries,veins and nerve fibres (Plate VI, f i g * 12 i ) are soattered in the lamina propria* The musoularis externa consists of two layer, an inner longi-tudinal, and an outer oiroular smooth muscle layer* In cross section the muscle oells appear to be of differnt shapes and sizes t i g h t l y paoked within a bundle and enolosed i n a connective tissue sheath (Plate VI* f i g * 12 a)* The nuolei are plaoed centrally, sometimes within a clear colorless vaouole (Plate VI, f i g 12* )• Usually, one nuoleolus and a peripheral chromatin net are v i s i b l e * Eaoh o e l l of a bundle i s surrounded by reticulum and eaoh bundle is enveloped in retioular fibres* The oiroular musole consists of long spindle shaped oells lying parallel to one another* Their oval nuolei are plaoed i n the widest part^of the o e l l * Short retioular fibres oan be seen more clearly i n a longitudinal seotion of the musole* The musole bundles are held together by oonneotive tissues interlaced with elastic fibres* Through this connective tissue layer and especially at the bases of the esophageal ridges are small blood vessels and nerves* Enveloping the entire tube is the tunica adventitia whioh oonsists of dense collagenous fibres and contains large blood vessels, and capillaries* Nerve fibres and autonomic ganglia supplying the esophageal wall are observed at intervals in the adventitia, California murre ( Uria aalgae californioa) The esophagus of the California murre resembles generally that of the kingfisher (Plate III* f i g * 4)* The wall is thrown into longitudi-nal wavy folds that gradually smooth out at the junction of the esophagus with the proventrioulus* The heavy folding provides for greater distension than was possible i n the kingfisher* The usual three ooats contribute to the structure of the wall} a mucosa* musoularis externa, and a tunioa adventitla (Plate VII, f i g . 14)* The epithelium i n this bird i s considerably thicker extending fifteen to sixteen c e l l layer, or more i n places* The oell3 of the germinative layer are small and heavily staining with their nuolei f i l l i n g most of the body. These nuclei l i e close together in the germinativum but toward the free surface take on various shapes (Plate VIII, f i g . 16 e). Cornificatioh oan not be observed anywhere* A slight flattening is present in some plaoes, but i t is more usual to see the oells at the surface swollen or enlarged (Plate VIII, f i g . 16 e). Oooassionally atrophication of the nuolei with subsequent sloughing o f f of the oells ooours. The esophageal glands l i e in the lamina propria with only their excretory duots extending through the epithelium (Plate VIII, f i g . 16 a,b). The oells lining the secretory tubule are t a l l , very narrow columnar oells - 16-with basal nuolei and granular cytoplasm (Plate VIII, f i g , 16 d). The excretory duct oells are ouboidajL almost round to oval in shape, and possess round nuclei (Plate VIII, f i g 16 b). These oells resemble the gland cells of the kingfisher. The cytoplasm i s lighter staining than that of the basal gland oells, and i s less granular. A dense collagen layer well supplied with blood vessels and lymphooytes, singly or in groups, constitutes the lamina propria which projects upwards into the epithelium by prominent papillae. The f i b r o -blasts of the connective tissue are outstandingly abundant, and sli g h t l y compressed in shape. Many elastic fibres interlace with the collagenous fibres (Plate VIII, fig.17 b). No structure comparable to the musoulais mucosa oould be observed, and the submucosa could only be differentiated a r b i t r a r i l y . The connective tissue of the lamina loosens at i t s junction with the musoularis externa, elastic fibres inorease and blood vessels beoome more numerous. This layer extends to surround the muscle bundles of the externa. The musoularis externa consists of an inner longitudinal band, and an outer oircular band of smooth musole. The bundles are of varying sizes surrounded by collagenous and elastic fibres. The muscle oells are homogenous throughout the cytoplasm, with nuclei exoentrically placed. There was no vacuolation present within the f i b r e , as in the kingfisher (Plate VI, f i g , 12), The nuclei are thinner and more elongate, in fact, the muscle oells themselves are smaller (Plate VI, f i g 13), Toward the junotion of the esophagus with the proventrioulus a third layer of muscle appears in the form of small longitudinal bundles dispersed in the tunica adventitia. - f 7-The tunica advent i t ia is a heavy layer of -white connective tissue containing nerve fibres and ganglia of the autonomic nervous system that innervate the esophageal wall. Blood vessels of different sizes are also present in this layer* Surrounding the adventitia i s a thin mesothelium* Soreeoh owl (Otus aslo kennlootti) .Short-eared owl (Aslo flammeus flammeus) The esophagus of the screech owl l i e s to the right (Plate II, f i g * 2 ) and is comparatively shorter than that of the other birds studied. TTone of the specimens examined showed any evldenoe of crop-like dilation (Plate III, fig.5 )• Throughout i t s length the wall i s f a i n t l y ridged, and thinner than in the kingfisher or murre (Plate IV, f i g . 9; Plate VII, f i g . 14; Plate IX, f i g . 18). As in the kingfisher and murre, the wall i s composed of three coats (Plate DC, f i g . 18). A thin epithelium of about six or seven o e l l layers covers the ental surface of the esophagus. The germinativum layer is mot very prominent. Cornification occurs slightly over the whole surface. In the short-eared owl the epithelium is about two times as thick as in the screeoh owl, and i t does not show any oornification (Plate X, f i g . 21 e). . The esophageal glands l i e on a basement membrane (Plate XI, f i g . 22 a) in the upper limit of the lamina and extend a l i t t l e into the epithelium (Plate IX, f i g * 19 )* They are in the soreeoh owl (plate X, f i g . 20) simple oval shaped glands with very short excretory duots, while in the short-eared owl, the duots are considerably longer -f 8-(Plate X, f i g * 21)* The basal gland oells are t a l l , columnar and narrow, thickening sli g h t l y as they approaoh the excretory duct* These glands resemble those found in the kingfisher (Plate V, f i g . 11; Plate Z, f i g . 20, 21) differing chiefly in .the lengths of $he excretory duct. In the screech owl the ducts are almost non existent, while in the short-eared owl they approach the size observed i n the kingfisher. In the owls^re^a' l i t t l e more alveolar i n shape and do not extend as far into the lamina propria. The lamina propria i s formed of dense white connective tissue with-a few compressed fibroblasts. Lymphocytes are rather soaroe. Within the lamina, blood vessels pass to supply the wall. A musoularis mucosa is missing, and the submuoosa consists of merely a continuation of the lamina that joins the musoularis externa. Two smooth muscle layers make up the musoularis externa; an inner longitudinal and an outer circular layer. The circular muscle i s about two times as thich as the.inner longitudinal musole. These are held together by a loose oonnoetive tissue interspersed with elastio and retioular fibres. Surrounding the tract i s a tunioa adventitia, i n whioh blood vessels and nerves are contained (Plate IX, f i g . 18 d,)'. Peale's falcon (Faloo perigrlrius pealei) Sparrow hawk (FaICQ sparverius sparverius) Pigeon hawk (Faloo oolumbarius suekleyi) The esophageal tube of Peale's falcon (Plate III, f i g * 6) shows a distinct enlargement at i t s anterior region a short distance behind the g l o t t i s . This enlargement or expansion i s observed in a l l of -19-the specimens studied and may be referred to as the orop* At this point the ental surface of the wall is heavily and irregularly folded, but as the esophagus passes posteriorly the folds converge into longitudinal one8 that remain as such for the rest of i t s length* The sparrow hawk, and the pigeon hawk (Plate III, f i g * 7, 8) show essentially the same struoture as the falcon* The usual three coats observed in the other birds make up .the struoture of the walls(Plate XII, fig*23)* A musoularis muoosa i s onoe again entirely missing, and the submuoosa can not be definitely placed* The epithelium generally resembles skin and is thicker than any other so far seen, approaching up to twenty-five and t h i r t y c e l l layers* A definite arrangement of transitional c e l l types is apparent (Plate XIII, f i g . 26). The oells of the stratum Malpighii (Plate XIII, f i g * 26 a) are densely arranged perpendioularly. to the lumen. The cel l s of the middle layer beoome less compressed, their nuclei approach a spherioal shape and appear to occupy a small part of the c e l l . In the surface layer the oells are highly flattened and the epithelium is very irregular. Cornification (Plate XII, f i g . 23 a) is present along the whole inner surface of the esophageal wall. The epithelium is of about equal thickness in the falcon, sparrow hawk (Plate XVII, f i g . 33) and pigeon hawk. It is irregular i n the falcon and more heavily cornified than in the sparrow hawk. The pigeon hwak does not show extensive oornif-ioation either. The lamina propia joins the epithelium by prominent and elongate papillae. These are regularly placed in the pigeon hawk. The lamina consists of a dense layer of collagenous fibres that extend from - 20-the epithelium to the musoularis externa* Elastic tissue i s most abundant nearest the epithelium* The fibres are so short and thin that i t was very d i f f i c u l t to obtain a dear picture with Verhoeff's elastic stain* Either too much stain was removed from the fibres obtaining no result, or too much remained in the slide producing a black picture* Embedded within the lamina are the glands of the esophagus* (Plate XII* f i g * 24; Plate XIII, f i g , 25)* These are not simple glands as observed in the previous birds, but are large lobulated structures with the smallest in the pigeon hawk, and the largest appearing in the falcon. Surrounding the glands i s a capsule of dense connective tissue, o The gland oells are ridged with capillaries, and primary gland oells that extend into the ridges at regular intervals to give the gland i t s • lobulated appearance (Plate XIV, f i g , 27), The gland oells s i t on a distinot basement membrane. They are t a l l oolumnar ce l l s (Plate XIV, f i g * 27 a) possessing f a i n t l y granular networks in their oytpplasm and small basal nuclei* The oells are of the holoorine secretory type, and after a meal are entirely absent from the wall (Plate XVI, f i g , 32)* Prom birds,shot at the time of feeding, various stages in secretion are observed. At the beginning of the secretory cycle, the apex of the gland c e l l breaks down. first,with a liberation of the cytoplasmic granules following (Plate XIV, f i g , 28)* As the o e l l becomes depleted of i t s cytoplasm (Plate XV, f i g * 29) the nucleus and the remainder of the oell cytoplasm starts to move toward the lumen, leaving a few low ouboidal gland oells, blood c e l l s , and lymphocytes at the basement membrane* As the nuclei move toward the excretory duct (Plate XVI, f i g * 31) of the gland, they disintegrate and pass out with the cytoplsmic secretion into the esophagus (Plate XV, f i g * 30 o). The sebretory duct i s lined by squamous epithelium (Plate XV, f i g . 30 b ) and tends to close as does the space (Plate XVII, f i g . 31 c) l e f t after the gland completes secretion. An atrophied, almost indistinguishable gland lobule remains within the lamina together with a few blood vessels, and lymphooytes (Plate XVI, f i g . 32 o,e). This oondition maybe observed in the esophagus of the bird shortly after the oompletion of a meal. Regeneration appears to take place from these indifferent or primary ce l l s (Plate XVI, f i g 32 d). A similar situation is present in the sparrow hawk (Plate XVII, f i g . 34 ) and pigeon harwk • The suhmuoosa or continuation of the lamina propria joins the musoularis externa whioh oonsists of two smooth muscle layers; an inner longitudinal one, and an outer ciroular one. The musole layers are exceedingly thick in the sparrow hawk. A serosa of dense connective tissue surrounds the entire tube. Proventriculus -Kingfisher (Megacercyle alcy_pn caurina) A f t e r i t s junction with the esophagus the proventriculus bends dorsally to enter the gizzard from the l e f t side (Plate I , f i g . 1£). The longitudinal folds of the esophageal v a i l converge into 8 or 10 heavy rugae. The proventricular wall thickens from approximately 1.7 m,m, to 5.2 m,m. T a l l columnar epithelium gradually supercedes the s t r a t i f i e d squamous epithelium of the esophagus. A stroma of connective t i s s u e , the lamina propria, supports the epithelium. Within the lamina propria, a very diffuse musoularis mucosa may be detected at various points. The submucosa extends to surround the deep glands of the proventriculus and to j o i n the musoularis externa. The musoularis externa i s composed of a: inner l o n g i t u d i n a l , middle c i r c u l a r , and a t h i r d l ongitudinal smooth muscle layer. The entire tube i s enclosed i n a t h i n tunica adventita (Plate XIX, f i g . 36), Macroscopic examination of the mucosal shows i t to covered by a soft velvety l i n i n g that i s pierced by minute p i t s . These p i t s form the gastric crypts or foveolae gastricae of the mucous membrane. The surface epithelium of the crypts consists of simple t a l l columnar c e l l s possessing large spherical n u c l e i that f i l l the majority of the basal part of the c e l l . The c e l l i s divided by a d i s t i n c t l y granular l i n e i n to approximately two halves. The basal part possessing a spherical v.. nucleus surrounded bya dense granulation and a bulbous a p i c a l part that i s f a i n t l y granulated. The c e l l s stained r e a d i l y with carmine fo^mucus. These c e l l s s i t on a basement membrane that connects them -23-to the lamina propria. The lamina propria consists of dense collagenous and r e t i c u l a r f i b r e s and extends i n t o the ridges between the gastric crypts containing i n i t many small c a p i l l a r i e s that supply the epithelium. Scattered d i f f u s e l y throughout the lamina propria are smooth muscle bundles.of varying sizes (Plate XX, f i g . 37c). These make up the musoularis mucosal layer of the proventricular w a l l . The submucosa passes from the musoularis to surround the deep proventricular glands (Plate XX, f i g . 37). The connective tissue of t h i s layer becomes much denser and forms a capsule that encloses the glands. The f i b r o b l a s t s are compressed and elongated. Microscopically, the glands appear as simple lobes arranged side by side i n the submucosa (Plate XXI, f i g . 39). Upon microscopic observation each lobe i s seen to be composed of many simple tubules that radiate from several exccet -ory ducts (Plate XX, f i g . 37). Surrounding each tubule i s a continuation of the reticulum present i n the outer capsule of the lobe. The excretory ducts are continuations of the gastric crypts i n t o the deep glands. The c e l l s l i n i n g the excretory ducts are simple columnar c e l l s s l i g h t l y smaller than the neck c e l l s of the gastric mucosa, and do not y i e l d a charac t e r i s t i c s t a i n f o r mucus. They show an elongated nucleus placed almost c e n t r a l l y within the c e l l and a cytoplasm that gives a l i g h t e r non-granular s t a i n than the neck c e l l s of the crypt. The secretory lobules are composed of a single layer of cuboidal granular zymogenic c e l l s (Plate XX, f i g . 38c). The nu c l e i are spherical containing a very regular chromatin pattern. The posi t i o n of the nucleus depends upon the a c t i v i t y state of the c e l l and may be central or basal. -24-The musoularis externa consists of three layers of smooth muscle, an inner longitudinal band, a larger c i r c u l a r band, and a t h i r d l ongitudinal layer of small bundles scattered i n the dense connective tissue of the lamina adventitial, • C a l i f o r n i a friurre (Uria aalgae C a l i f o r n i a ) As the esophagus approaches the proventriculus, i t s longitudinal folds converge!from twelve to seven folds or p l i c a e . The plicae are deeper and more pronounced than those seen i n the kingfisher. The esophageal v a i l increases gradually u n t i l a thickness of 5 mm. i s reached at the middle of the proventriculus.. Only about one half of t h i s thick -ness contains proventricular glands. • The s t r a t i f i e d squamous epithelium i s soon replaced by simple columnar epithelium (Plate XXIII, f i g . 41d) that l i n e s the gastric crypts i n a single row. The crypts are denser than those i n the kingfisher (Plate XXII, f i g . 40a). The tunica, propria i s much reduced between the gastric mucosa and the glands. The layer consists of dense collagenous and r e t i c u l a r fibres, (Plate XXIV, f i g . 43g). Present also within t h i s layer are small blood vessels and nerves. A diffuse muscularis mucosa as observed i n the kingfisher can be detected except that i n t h i s b i r d the muscle bundles continue inrsthe connective tissue between the glands (Plate XXII, f i g . 40c). The i n t e r l o b u l a r spaces are considerably increased and the proventricular glands are pushed nearer to the lumen of the proventriculus. The lamina propria i n t h i s case extends to surround the proventricular glands leaving the submucosa as a small region of loose connective tissue between the deep glands and the muscularis externa. Contained -2 5-i n t h i s layer are many small blood vessels and nerves regularly arranged i n the gastric ridges between groups of glands present i n each ridge (Plate XXIV, f i g . 43e)* The gland lobes are alveolar rather than tubular i n shape and the central excretory cavity i s much large r . The i n d i v i d u a l c e l l s of the mucosal, secretory, and excretory regions do not show much variation from those of the kingfisher. The zymogenic c e l l s of the murre (Plate XXIII, f i g . 42b) are, smaller than those found i n the king - f i s h e r and riot,as c l o s e l y situated so that i n a cross section of a tubule the d i s t a l parts of the c e l l are not i n contact but produce a serrated appearance. The muscularis externa consists of the three smooth muscle layers, an inner l o n g i t u d i n a l , a middle c i r c u l a r , and a diffuse outer longitudinal one scattered i n the tunica adventitia (Plate XXII, f i g . 40f). A peritoneum covers the whole organ. Screech owl (Otus asio kennicotti). S h o r t - e a r e d owl (flsio f l a m m e u s yi&rnmfcu.t.V As the esophagus passes i n t o the proventriculus, the v a i l of the t r a c t thickens gradually from 0.7 mm. i n the esophagus to 2.3 mm. at the middle of the proventriculus. The folds of the esophagus smooth out and no heavy f o l d i n g of the proventricular m i l can be observed. The l i n i n g i s f a i n t l y wrinkled and pierced by small p i t s . As i n the esophagus, three coats contribute to the structure of the m i l ; a mucosa, a muscular - i s externa, and a tunica adventitia. A muscularis mucosa i s missing (Plate XXV, f i g . 44). A single layer of t a l l columnar epithelium l i n e s the gastric p i t s of the mucosa. The e p i t h e l i a l c e l l s are divided into a mucus staining a p i c a l region and a paler basal part (Plate XXV, f i g . 45a). The crypts are not regularly shaped as observed i n the kingfisher and murre but are i r r e g u l a r (Plate XXV, f i g . 45) and show some branching. In the short-eared owl the crypts are deeper and more regular i n appearance, resembling somewhat the condition i n the kingfisher. A tunica ppropria, heavily i n f i l t r a t e d with lymphocytes and consisting of dense white collagenous f i b r e s forms a supporting tissue that extends from the epithelium to surround the deep proventricular glands. Immediately adjoining the glands the connective tissue tbecomes very dense i n the form of a capsule around the lobe. The glands possess the same general structure; a single lobe composed of many tubules radiating about a branched excretory duct (Plate XXV, f i g . 451). The zymogen gland c e l l s are s l i g h t l y larger than i n the murre and produce a d i s t i n c t l y serrated appearance (Plate XXVJ, f i g . 46b). The excretory duct joins the gastric crypt (Plate XXV, f i g . 45d) through which secretion takes place. A thin submucosa joins the lamina propria to the muscularis externa and extends f o r a short distanca between the gland;; lobes. Within the submucosa and occuring at regular i n t e r v a l s between two adjacent lobes are a nerve,.a vein, and an artery. The submucosa joins the muscularis externa (Plate XXV, f i g . 441) which consists of a large inner lon g i t u d i n a l layer, a larger c i r c u l a r middle layer and f i n a l l y a few lon g i t u d i n a l bundles scattered throughout the serosa. Passing from the serosa through the muscularis to the glandular layer i s an i n t r i c a t e nerve plexus, the myenteric plexus of the stomach. Ganglia (Plate XXVI, f i g . 47c) are arranged at regular int e r v a l s i n the tunica adventitia with f i b r e s and nerve c e l l s passing through the muscularis to supply nervous innervation to the glands and the muscular wall. A thin mesothelium surrounds the entire tube. Peale's falcon (Falco peregrinius peal&i) Sparrow hawk (Falco sparverius sparverius) Pigeon hawk (Falco columbarius suckleyi) The folds of the esophagus converge to form four heavy plicae in the wall of the proventriculus. The surface mucosa, possess a soft velvety appearance. The crypts in the mucosa.are regular and placed one beside the other, thus reducing considerably the tunica propria (Plate XXVII, f i g . 48a;b). This layer extends slightly between the gland?lobes while the lobes are pushed close to the bases of the gastric crypts (Plate XXVIII, f i g . 50). An identical situation can be observed in the sparrow hawk (Plate XXIX, f i g . 51), while in the pigeon hawk the gastric crypts are considerably reduced and the tunica propria is increased* The tunica extends around the glands as a thin capsule of dense connective tissue. No muscularis mucosa is present. The glands are longer and narrower and they cover a greater area than In the other birds. In the falcon the wall is 6 mm. thick and i t is almost entirely composed of glandular material. In the sparrow hawk the glands are smaller* The tunica propria is reduced and the muscle layer is a thin band surrounding the tube. From the gastric cryptsoone secretory duct extends into the centre of each tubular lobe of the deep proventricular glands (Plate XXVIII, f i g . 50d,e). Around this.duct the secretory tubules radiate. In the sparrow hawk the lobes are more -28-alveolar in shape (Plate XXX, fi g . 52c) . The cells of these tubules are closely arranged with a l l parts of one cell in contact with the adjoining cell reducing the lumen of the tubule (Plate XXVII, f i g . 49b). The tubules are not as dense in the sparrow hawk and the zymogen cells are smaller (Plate XXX, fig * 53a,b). The submucosa is*very small region joining the glands to the muscularis externa. The muscularis externa is reduced to thin bands of longitudinal and circular smooth muscle with additional longitudinal bundles scattered in the serosa* In the sparrow hawk the inner longitudinal muscle passes slightly between the gland lobes (Plate XXIX, f i g . 51d) but in the pigeon hawk a large middle circular band of muscle is present and the inner longitudinal bundles do not enter between the lobes. A tunica adventitia surrounds the tube* -29-'Gizzard Kingfisher (Megacercyle alcyon courina) In the kingfisher the proventriculus enters the gizzard from the left dorsal side* The gi zzard enlarges ventrally to f i l l the left and greater part of the right abdominal cavity. (Plate I. f i g . 1) Sside the entrance of the proventriculus and slightly to the right the duodenum leaves the gizzard. Externally a small swelling of the gizzard wall takes place and the intestine passes to f i l l the remaining part of the right cavity. Internally a sphincter consisting of five bulbous muscular projections covered by the keratinoid lining of the gizzard guards the exit of the duodenum. (Plate XXXI, f i g . 5h) From the liver, the falciform ligament continues along the ventral median and slightly left wall of the gizzard to join the mid ventral body wall and inner surface of the sternum, and divides the abdominal cavity into right and left regions. (Plate I. f i g . lg). This continuation of the falciform ligament is often compared to the greater omentum of mammals, but is not homologous to that structure (Hyman 19ii7). "The ligament;'layman (19^7) P. 283) says, "is a mesentery peculiar to birds and arises as a secondary outgrowth from tie serosa of the gizzard, to the ventral body wall and is probably due to the need for additional support for the heavy gizzard." The wall of the gizzard thickens on the dorsal and ventral sides and becomes irregularly folded (Plate XXXII, fig * S>8: Plate XXXIII f i g . 59)* The soft velvety lining of the proventriculus i s soon replaced by the hard keratinoid lining of the gizzard. A single layer -30-of long simple tubular glands (Plate XXXIV, f i g * 60 a) secretes the lining* The glands are present i n the lamina propria and they connect with the pits of the gastric muscoa. Lining the crypts of the glands are low columnar or cuboidal c e l l s (Plate XXXIV f i g * 60 b), providdd with basal nuclei and granular cytoplasm* From these c e l l s the kez— atijioid secretion of the gizzard i s poured into the lumen of the gland (Plate XIDdV, f i g . 60 c ) . As the secretion reaches the surface i t joins with that of the adjoining glands to form the hard continuous layer and presents striations representing the contributions of each glandular lumen* Within this layer BO me c e l l u l a r debris can be ob-served* The lamina propria (Plate XXXIV f i g * 60 d) surrounds the glands of the gizzard and only extends far enough to connect with the band of smooth longitudinal and circular muscle, or muscularis mucosa (Plate XXXIV, f i g * 60 e), or immediately below the glands. A submucosa of appreciable size joins the mucosa to the muscularis externa* The muscularis externa i s a thicker layer than that observed i n the esophagus or proventriculus. A heavy inner smooth longitudinal layer that extends into the folds present i n the gizzard composes a part of the muscularis externa. The circular muscle band i s increased considerably and each bundle i s surrounded by a connective tissue of collagen and elastic fibres. The entire gizzard wall i s abundantly supplied with blood Vessels. Present within the muscle bundle (Plate XXXV, f i g * 61 a) close to the serosa, are large bundles of nerve fibres dispersed at intervals throughout the circumferance of the gizzard* Fat,blood vessels, and muscle bundles enclosing more nerve fibres compose the tunica adventitea. A mesothelium surrounds the tube. California triurre - (Uria aalgae californica) The proventriculus enters the gizzard which continues for a short distance as a tube, before expanding into the bulbous structure of the gizzard. In this species muscular development (Plate XXXVI, f i g . 62, 63) is quite marked with greatest increase in muscular thick-ness occurring on the dorsal and ventral sides. Between these two regions extends the narrow lumen of the gizzard. Beginning at the proventriculus and continuing around the cavity of the gizzard, the muscles become very thin on the lateral sides (Plate XXXVI, f i g . 63) Beside the entrance of the proventriculus into the gizzard, the exit of the duodenum is situated. & sphincter (Plate XXXI fi g * 55) consisting of a band of muscle surrounds the duodenal exit. At the right a slight bulging of the gizzard wall takes place. The keratinoid lining i s thinner and greatly wrinkled. This may be the pyloric pocket that "Cazin (I887) has described for some water birds. ' A mucosa, muscularis externa and a serosa make up the structure of the,,wall (Plate XXXVII, f i g . 6k)* A similar type of long simple tubular gland as observed in the kingfisher is present in this bifd. The glands possess essentially the same structure and appear to be of approximately the same size as those found in the kingfisher, but the keratinoid lining i s about five or six times as thick (Plate XXXVII, f i g . 6k a). -32-A simple cuboidal epithelium (Plate XXXVIII, f i g . 65 b) covers the cyrpts of the gizzard glands. The cells possess large spherical nuclei and a granular cytoplasm. Surrounding the glands is a much reduced tunica propria which joins almost immediately a layer of smooth circular and longitudinal muscle bundles. Small blood vessels are present in the tunica at the bases of the glands, A complete layer of submucosa surrounding the tunica propria i s not present. Instead, the tunica propria appears to intermingle with the muscle bundles, especially in the ridges that form the plicaa of the gizzard. The fibroblasts of the tunica propria and submucosa are more abundant and not as compressed as those observed in the other part os this digestive tract. The muscularis externa is greatly increased in some daces, particularly where folds (Plate XZXVTI, f i g , 6k d) of the gizzard wall are present. At these points the smooth muscle bundle s extend into the ridges to the submucosa. The inner longitudinal muscle is of various thicknesses, while the outer circular layer is quite regular. Between the muscle bundles, blood vessels pass in the connective tissue sur-rounding these bundles, A serosa encloses the entire gizzard. Screech Owl - (Otus asio kennicotti) After its junction with the proventriculus (Plate II, f i g , 2 i ) the gizzard in the owl passes into the abdominal cavity and f i l l s the left side almost completely. From tte right anterior region the duod-enum leaves to join the remainder of the intestine which f i l l s the right side. -33-The thickndss of the giazard wall in this species varies to some ex-tent. A thin layer of keratin lines the ental surface of the gizzard, the muscularis externa at some points is reduced (Plate XXXIX, f i g . 66 d) and a Iyer of fat envelops the exterior surface. The duodenal exit is slightly posterior to the entrance of the proventriculus. A sphincter (Plate XXXI, f i g . 55) consisting of a mere puckering of that region guards the exit of the duodenum. The wall is composed of essentially three coats, a mucosa, muscularis externa and a tunica adventitia (Plate XXXIX, fig * 6 6 ) . The proventricular glands end abruptly. The epithelium (Plate XL, Fig. 67 a) continues for a short distance and gradualy changes to the epithelium of the gizzard (Plate XLI, f i g . 68 a). The simple tubular gizzard glands with slightly bulbous basal regions are•arranged side by side in the lamina propria. These glands join to the pits in the mucosa and through this neck region they sec-rete into the lumen of the gizzard. The cells of the glandular crypts are the usual cuboidal or low columnar epithelium, with spherical nuclei, whereas the cells of the neck and apical regions of the mucosal folds are of the t a l l columnar type. The glandular cytoplasm is granulated. Also present within these cells are large' colorless spheres, observed especially above and below the nucleus in the apical columnar cells, (Plate XLI, fig* 68 f ) . The tunica propria composed of dense collagenous tissue and abundantly supplied with fibroblasts, unites with the muscularis externa. A submucosa i s absent. The muscularis externa consists of an inner longitudinal smooth muscle layer and an outer circular muscle area which i s greatly thickened at various points (Plate XXXIX, f i g . 66 d). Nerve fibres occur frequently within'.the gizzard $uscle and ganglia are present in the tunica adventitia. The tunica adventitia oomposed-of collagenous fibres and far surrounds the entire tube. Peale's falcon (Falco peregrinius pealei) Sparrow Hawk (Falco sparverius sparvarius) Pigeon Hawk (F alco columbarius suckleyi) ' The gizzards of the Peale's falcon, sparrow hawk and pigeon hawk are more spherical in shape than those observed in the other birds. (Plate III figs. 6 , 7 , 8 ) . The proventriculus enters the gizzard from the posterior side. Beside this entrance and to the left is the exit of the duodenum. In the Peale's falcon a sphincter (Plate XXXJ, f i g . 57) , comppsed of two bulbous structures on one side and a fold of the wall on the other side, guards the opening to the duodenum. The muscular wall is reduced to a minimum, and the soft lining of the proventriculus is rapidly replaced by the keratinoid lining of the gizzard. Three coats contribute to the structure of the gizzard wall| a mucosa, muscularis externa and a tunica adventitia, (Plate XLII, f i g . 6 9 ) . The proventricular glands are soon replaced by the simple tubular glands of the gizzard which join the surface gastric pits. The surface pits are covered by simple t a l l columnar cells, whose cyto-plasm is distinctly divided into an apical pale, granular, cup-like -35-region, and a basal heavily granulated area, slightly above and below the nucleus, (Plate XLIII, f i g . 70 c). Surrounding the glands is a loose collagenous and reticular area and enclosing small groups of glands is a dense band of connective tissue (Plate XLII, fig* 6° d) beneath which lies the submucosa. Essentially the same structure as in the falcon is observed in the sparrow hawk. The glands are grouped by a dense connective tissue band, but not in as pronounced a manner as in the'peale's falcon, (Plate XLIV, f i g . 71 d). In the pigeon hawk the connective tissue band is not observed. The glandular cells are low cuboidal cells lining the crypt of the gland in a single row (Plate XLV, f i g . 72 b). The muscularis externa is greatly reduced in the falcon, whereas in the sparrow hawk and th? pigeon hawk i t is quite large. In the sparrow hawk i t is composed mainly of a long-itudinal band of muscle (Plate XLIV, f i g . 71 e) a i j w h v s j f e . .s are thrown into heavy plicae. Penetrating the muscle are many blood vessels and nerves. The serosa is thick and contains larger blood vessels and nerve fibres. CONCLUSIONS AND SUMMARY In the kingfisher, California murre, screech owl and the short-eared owl, the esophagus consists of a simple, thin-walled, greatly expansible tube of generally even calibre, while in the Peale's falcon an anterior enlargement that corresponds 1 to or forshadow© ; the fully developed crop of gr^pivorous birds, is present. The wall possesses the usual structure characteristic of this region, & stratified squamous epithelium, a tunica propria and a muscularis externa composed of two layers of smooth muscle. The wall is generously supplied with glands and several gland types are present. In the Kingfisher, screech owl and short-eared owl, oval glands composed of essentially the same type of cuboidal cells are situated in the epithelium with only a small portion of the basal part of the gland extending into the tunica propria. The excretory duct in the screech owl is short and nearly indistinguish -able, while in the short-eared owl and kingfisher, the ducts are quite long. In the califonnia murre the glands are s t i l l oval in shape, but have sunkc. \ below the epithelium into the connective tissue of the; lamina propria with only the excretory ducts passing through the epith-elium. The gland cells in this bird have become very narrow, t a l l col-umnar cells, thickening and shortening as they united with the low cuboidal cells of the excretory duct. In the Peale's falcon, sparrow hawk and pigeon hawk, a different type of gland can be recognized. Large lobulated glands rather resembling the esophageal glands of the hen (Calhoun 1933) and composed of t a l l columnar mucous secreting cells like those found in the murre are observed. The excretory duct cells are squamous cells of the epithelium, Schreiner (1900) found that i f the number of glands in the esophagus increased too greatly, they tended to remove themselves fjw»/the" surface area and sink to the under-lying connective tissue. The cells of the excretory ducts would lose their secretory capacity. The glands in the Peale's falcon, sparrow hawk and pigeon hawk are holocrine secretory and sometimes are en-tirely absent frorijthe esophageal wall. With mucicarmine, a character-istic colour for mucus is obtained for a l l of the esophageal gland cells, including the excretory duct cells of the kingfisher, owls and murre. According to Schaffer's (192ii) classification,all of the glands are of the homocrine monoptychial type. Essentially two methods of secretion, apoctine and holocrine for lubricating the food that passes through the esophagus., are dis-tinguished. In apocrine secretion, present in thejkingfisher, owls and murre, a continual secretion of mucus by the breakdown of the apical parts of the gland cells and in the holocrine type elimina-tion of the entire gland content, including nuclei and cytoplasm occurs. This holocrine secretion is characterized by the Peale's falcon, sparrow-and pigeon hawk. It would be difficult to state which of these two methods of secretion is more effective. In the apocrine type, secre-tion is always present while in the holocrine type, time is necessary for the regeneration of the gland. When the food of these birds is considered, i t will be noted that the diet of each bird is essentially flesh. The kingfisher vive-a chiifly on fish, while the murre will eat crustaceans in addition. - 3 6 -(Taverner, 19U7). The owls are generally predators on small mammals (Taverner^19U7) and the Peale's falcon and pigeon hawk eat birds (Taverner,19U75 May 1935)• The sparrow hawk feeds almost entirely on insects (Taverner, 19h7)» Although as stated above,, the chief food of these birds is; meat of one kind or another, considerable variation Aexists, especially in the structure of the esophagus. In the kingfisher, owls and murre, apocrine glands of similar cellular structure occur, yet the Peale's falcon and pigeon hawks, although they show a preference for birds, bol^  will also eat small mammals, as do the owls, but have an entirely different glandular structure. Their glands are deeply sunkf.;i into the tunica propria and the excretory duct cells are transformed so that they resemble or are the cells of the epithelium. May, (1935), found that hawks were able to go a considerable length of time without eating and that many adult hawks did not capture food more than once in two or three days. The feeding habits thus maybe a significant factor in the type of glandular cell present. The stomach of the bird is divided into two regions, an anterior glandular proventriculus and! a posterior muscular gizzard. The stomach shows less variation in structure than the esophagus. The proventriculus is characterized by the presence of peculiar glands that are found generally in the stomachs of a l l birds. These are composed of masses of simple tubules placed adjacently to each other and radiating in a l l planes about a central excretory duct. The tubules are lined by a single layer of •'zymogen" or digestive cells -39-that in the birds investigated are found to be a l l of the: same :: type. Slight variations from species to species can be observed! )only in compactness*, arrangement of tubules and in ce l l size The mucosa shows deep regular crypts and a reduced tunica propria in the kingfisher, murre, sparrow hawk and falcon, while in the o owl the crypts are irregularly branched, and the tunica propria is of appreciable size. A muscularis mucosa i s present in the kingfisher: and murre, but i s completely absent in the flesh-eating birds ( the owl, falcon, pigeon hawk and sparrow hawk). Friedman (1939) states that in birds, both acid and pepsin are elaborated by one c e l l . The author also observed only one type of c e l l . The gizzards generally possessed a keratinoid lining, a glandular layer that secretes the lining and a heavy smooth, muscular layer that is more or less uniform in size in the kingfisher, screech owl, Peale&s falcon and sparrow hank. In the murre modification of the gizzard takes place towardr the development of a grinding structure whereby the muscles develop heavily on the dorsal and ventral sides and the central cavity becomes considerably reduced. The keratinoid lining is thicker than that of the other birds, reaching almost the thickness present in the grain-eaters* It may be relevant to mention the Acarried out by Broussay (1935) in which sheftthe diet in a great horned owl from meat to vegetable; and produced an alteration in the gizzard structure. This change was not distinguishable from the outside, from the rest of the stomach. The gizzard became partly separated by a constriction from the rest of the stomach. The mucosa showed newly developed rugae -40-and longitudinal folds similar to those of a gizzard of a young grain-eating bird. As far as thm writer can determine no distinct relation can be drawn between the structure of the tract and the consistency of the food. Birds show considerable adaptability in their food habits. -4r-LITBRATURE CITED Babkin, B. P. 1944, Secretory Mechanisms of the Digestive Glands* Paul B. Hoeber Inc. Medical Book Department of Harper and Brothers, New York. Baker, J . R. a 1945. Cytological Technique. 2nd ed. Methuen and Co. Ltd, London Barthels, Phiiipp. 1895. Beitrag zur Histologie des Oesophagus der tfogel, Zs. f. wi»s. Zool. 59s 655-689 Bauer, Moritz. 1901. Beitrage zur Histologie des Muskelmagens der Vogel. Arch, f. micr. Anat., 571 653-676 Beddard, F. E. 1898. The Structure and Classification of Birds. Longmans, Green and Co. London. Bensely, R, R, and Bensley, S. H. 1938 Handbook of Histological and Cytologidal Technique. University of Chicago Press, Chicago. Bergmann, C. 1862. Einiges uber den Drusenmagen der Vogel. Arch. Anat. Physiol, wiss. Med., pp. 581-587 Berlin, W. 1852-53. Bijdrage tot de spijsvertering der Vogels. Nederl.Lancet, pp. 57-68 cited from Cazin, M. (1888) -42-Bodian, D. 1936. A New Method for Staining Nerve Fibres in Mounte d Paraffin Section. Anat. Rec.j 65: 89-97-Calhoun, M. L. 1933. The Microscopic Anatomy of the Digestive Tract of Gallus Domesticus. Iowa State Coll. J. Sci. 7, 1933 - 261-380. CQZXn, M. . ^ ^ ^ i : ^ d l d»-»\«H« rt.a^.ua. 1886. Recherches sur la Structure de l'estomac des oiseaux. C.R. Acad. Sci., 102:1031-1033. Cazin, M. 1887. Glandes Gastriques a mucus et a ferment chez les oiseaux. C.R. Acad. Sci., 104: 590-592. Cozin, M. 1888. Recherches anatomiques, histologiques, et embryologiques sur l'appareil gastrique des oiseaux. Ann. Des Sc. Nat. Zool., 7th Series, 4:177-323 Curshman, H. 1866 - Zur Histologie-des Muskelmagen der Vogel. Zs. wiss Zool., 16:224-235. Cited from Cozin (1888) Cuvier, G. 1805. Lecons d'anatomie comp. 2nd 8 V Paris, cited from Cozin, M. (1888) Darcus, S. J. 1930 Notes on the Birds of the Northern part of the Queen Charlotte Islands in 1927. Canadian Field Naturalist 44:45-49. Flovsr, I860. On the Structure of the Gizzard of the Nicobar Pigeon and other Granivorous Birds. Proc. Zool. Soc. pp. 330-336. Friedman, M. H. F. 1939* Gastric Secretion in Birds. J. Cell, and Camp. Physiol., V.13, No. 2 219-234. _ . Galigher, A. E. *^  ,J; J " 1934* The Essentials of Practical Microtechnique • Albert E. Galigher, Inc. Laboratory of Microtechnique. Berkeley, California. Garrod, A. H. 1872. On the Mechanisms of the Gizzard of Birds. Proc. Zool. Soc., London. April 16, pp. 525-529. Hasse. 1865. Beitrage zur Histologie des Vogelmagen. Zs. f. rat. Med., 28:1-31, cited from Cozin (1888) Home, E. 1814. Lectures on Comparative Anatomy. Lecture 3 and 4 (On the digestive organs of birds) cited from Bauer, Moritz (1901) Hunter, John 1786. Cited from M. Cozin(1888) Recherches anatomiques, histologiques, et embryologiques sur l'appareil gastrique des oiseaux. Ann. des Sc. Nat. Zool., 7th Series. 4*177-323. Hyman, L. H. 1947* Comparative; Vertebrate Anatomy, 8th Impression. The University of Chicago Press. Chicago, Illinois, Kaden, L, 1936. Uber Epithel und Brusen des Vogelschundes, Zool, Jahrb, Abst. Anat, u Out. 61 (4):421-466. Kingsley, J. S» 1926. Comparative Anatomy of the Vertebrates. P. Blakiston's Son and Co. Philadelphia. Klein, E. 1881 Esophagus und Magen in Strickers* Handbueh der Lehre von den Geweben des Menschen undobr Thiere., 1:497-539, cited from Cozin (1888) Lendrura, A. C. 1944. On the Cutting of Tough and Hard Tissues Embedded in Paraffin. Stain Tech. 19:143-144. Leydig, F. 1857. Lehrbucfi-der Histologied?s Menschen und der Thiere. Cited • ^ from Cozin, M. (188Q) Idllie, R, D. 1948 Histopathologic Technique, The Blakiston Co, Philadelphia, May, J. B, 1935. The Hawks of North America. The National Association of - 4 5 -Audubon Societies* H* Milne-Edwards, 1857-1881* Leoons sur la Bhysiologie et l'anatomie oomparee* ;cited from Cazin(l888) Molin, R. 1853* Sugle stomaohi delgi uooelli* Denkschr* Akad* Wiss*, Wien* 2 Abt. 3«l-24. 'eited from Bauer(190l) Pantin, C.F.A. 1946* Notes on Miorosoopial Technique for Zoologists* Cambridge University* Reaumur 1752* Cited from M* Casin, 1888* Recherches anatomiques, histologiques, et embryologiques sur l'appareil gastrique des oiseaux* Ann* des* So* Nat* Zool.* 7th Series, 4t177-323* Sohaffer, J* 1924* Zur Einteilung der Hautdrusen. Anfct* Anz* 57t353« ;Sited from Babkin(l944) Schreiner 1900. Beltrage zur Histologie und Embryologie des Vorderdarmes der Vogel in Ztsohr* Wiss* Zool* 68* xoited from Kaden(1936) -46-Sheer, B. T. 1948. Comparative Physiology. John w i l e y and Sons Inc. New York. Taverner, P. A. 1947• ^^irds of Canada. The Musson Book Company, Ltd., Toronto. Wiedersheim, R. E. 1872. Die feinern Strukturverhaltnisse der Drusen in Muskelmagen der Vogel. Arch. f. mikr. Anat., 8:435-452. • Wiedershsheim, R. E. and Parker W. N. 1907 Comparative Anatomy of Vertebrates. MacMillan Co., New York. HATE I Fig, 1 Relation of the digestive tract of the kingfisher to the surrounding area, a. Tongue b. Hyoid apparatus c. Esophagus d. Trachea e. Syrinx f. Bronchus g. Falciform ligament h. Liver (cut) i . Proventriculus j . Gizzard k. Duodenum 1, Ventral ligament m. Rectum a PLATE II Fig. 2 Relation of the digestive tract of the owl to the surrounding area. a. Tongue b. Hyoid c. Esophagus d. Trachea e» Syrinx f» Bronchus g. Falciform ligament h» Liver i» Proventriculus j . Gizzard k. Duodenum 1. Ventral ligament m. Rectum P L B T E 11 9 PLATE III Diagrammatic representation of the relative shapes of the esophagus and stomach ofr Fig. 3 Kingfisher a. Esophagus b. Crop evidence c. Proventriculus d. Gizzard e. Duodenum Fig. h California murre Fig. f? Screech owl Fig. 6 Peale's falcon Pig# 7 Sparrow hawk Fig. 8 Pigeon hawk. I PLATE IV Fig. 9 Kingfisher. Anterior esophagus. Mallory's triple 60X a. Epithelium b. Lamina propria c. Muscularis externa d. Tunica adventitia Fig. 10 Kingfisher. Esophagus. Haematoxylin and carmine ll|0X a. Epithelium b. Lamina propria c. Esophageal gland d. Longitudinal layer of muscular externa PLATE IV FIG. 10 PLATE V Figi 11 Kingfisher. Esophageal Oil immersion 1253X a. Basal gland cell b. Duct cell c. Nucleus d. Granular cytoplasm e. Epithelium f. Lamina propria glands. Mallory's triple. F (G. 11 PLATE VI Fig. 12 Kingfisher. Longitudinal muscle. Short foot method for silver impregnation of reticulum with Van Gieson counterstain 63OX a. Longitudinal smooth muscle bundle enclosed in a connective tissue sheath. b. Reticulum surrounding bundles of muscle c. Circular muscle of muscularis externa d. Short reticular fibres around each muscle c e l l e. Nucleus f. Clear area around nucleus g. Lamina propria h. Fibroblast i . Blood vessel Fig. 13 California murre. Longitudinal smooth muscle. Mallory's triple. 63OX a. Longitudinal smooth muscle b. Nucleus c. Loose connective tissue between the muscle bundles. FIG 13 PLATE VII. Fig* lit. California murre. Posterior esophagus. Mallory's triple. 60X a. Epithelium b. Lamina propria c. Muscularis externa d. Tunica adventitia Fig. 15 California murre. Esophagus. Haematoxylin and carmine ll*OX a. Epithelium b. Lamina propria c. Esophageal gland F IG. 15 PLATE VIII. Fig . 16 California murre. Esophageal glands. Mallory's triple 630X a. Basal gland cell b» Duct cel l c. Nucleus d. Granular cytoplasm e. Epithelium Fig. 17* California murre. Lauina propria. Verhoeff's elastic tissue stain LhOX a. Lamina propria b. Elastic fibres c. Fibroblasts d. Lymphocytes e. Artery f. Vein PLATE VIII FIG 17 PLATE IX Fig. 18. Screech owl. Esophagus. Mallory's triple 60X a. Epithelium b. Lamina propria c. Muscularis externa d. Tunica adventitia Fig. 1? Screech owl. Esophagus. Haemztoxylin and Carmine lUOX a. Epithelium b. Lamina propria * c. Esophageal glands PLATE X. Fig. 20. Screech Owl. Esophageal gland. Mallory's triple 630X a. Basal gland cells b. Excretory duct cells c. Epithelium d. Lamina propria Fig. 21 Short-eared owl. Esophageal gland. Mallory's triple 630X a. Basal Gland cell b. Duct cell c. Nucleus d. Granular cytoplasm e. Epithelium f. Lamina propria FIG.2T PLATE XI. Fig, 22. Screech owl. Esophagus. Short foot method for silver impregnation of reticulum . II4OX a. Basement membrane b. Reticulum surrounding the muscle fibres. J PLATE XI a b FIG. 22 PLATE XII Fig, 23« Peale's falcon. Anterior esophagus. Mallory's triple 60X a. Epithelium b. Lamina propria c. Muscularis externa d. Tunica adventitia Fig. 2 l u Peale's falcon. Anterior esophagus. Van Gieson 60X a. Epithelium b. Laaina propria c. Muscularis externa d. Tunica adventitia e. Esophageal gland PLATE XIII Fig. 25. Peale's falcon. Esophagus near the proventriculas* Haematoxylin and carmine LUOX a. Epithelium b. Lamina propria c. Esophageal gland Fig* 26* Peale's falcon. Epithelium. Verheeff's elastic tissue stain and eosin 63OX a* Stratum Malpighi b. Stratum corneum c. Lamina propria d* Fibroblasts e. Vein FfG. 25 FIG. 26 PLA.TE XIV Fig* 27• Peale's falcon. Gland before secretion. Verhaeff's elastic tissue stain and eosin 63OX a. Esophageal gland cell* . b. Primary gland cells c. Connective tissue capsule d. Capillary e. Lamina propria f. Fibroblast. Fig* 2 8 . Peale's falcon. Gland at beginning of secretion. Mallory's triple 63OX a. Esophageal gland cell b. Nucleus c. Beginning of the breakdown of the cytoplasm d. Vein e. Capillaries f. Primary gland cell PLATE XIV FIG. 28 PIATE XV. Fig. 29• Peale's falcon. Esophageal gland nearing end secretion. Haematoxylin and eosin 630X a. Connective tissue capsule b. Nuclei of gland cells c. Broken down cytoplasm Fig* 30 Peale's falcon. Esophageal gland secreting. Haematoxylin and eosin 63OX a. Glandular lumen lined with epithelium b. Squamous epithelium c. Glandular content being extruded d. Lamina propria papillae PLATE XV FfG.30 PLATE XVI Fig. 31 Peale's falcon. Esophageal glands at various stages .pf secretion. Showing the excretory cavity through the epithelium. Haematoxylin and eosin LUOX a. Esophageal gland. b. Tunica propria c. Blood vessels d. Excretory duct cut at various levels e. Space remaining after secretion. Fig» 3 2 . Peale's falcon. Esophagus after secretion. Verhoeffs elastic tissue stain 63OX a. Epithelium b. Lamina propria c. Blood vessel d. Primary gland cells e. Lymphocytes i PLATE XVII Pig* 33« Sparrowjhawk. Esophagus. Mallory's triple 60X a. Epithelium b» Lamina propria c, Esophageal gland d. Muscularis externa with contraction bands showing in the circular layer* Fig# 3U» Sparrow hawk. Esophageal glands. Haematoxylin and carmine 60X a. Esophageal gland b. Epithelium c. Lamina propria d« Fibroblasts PLATE XVTII Fig* 35* Sparrow hawk. Gland during secretion. Mallory's triple 630X A* Glandular epithelium. b. Connective tissue capsule PLATE XVIII FIG. 35 PLATE XIX Fig».36. Kingfisher. Proventriculus. Short Foot method for silver impregnation of reticulum and Van Gieson 60X a. Epithelium b» Lamina propria c» Muscularis mucosa d» Deep proventricular gland e. Submucosa £• Longitudinal smooth muscles f. Circular smooth muscle d e f FIG. 36 S PIATE XX Fig. 37• Kingfisher proventriculus. Mallory's triple lUOX a. Faveolae gastricae b. Lamina propria c. Muscularis mucosa d. Submucosa e. Deep proventricular gland f. Central collecting ducts g. Capillary Fig. 38 Kingfisher. Deep proventricular gland tubules. Mallory's triple. 63OX a. Cross section of tubule b. Reticulum surrounding lobule and containing blood capillaries. c. Zymogen cell d. Nucleus (chromatin pattern very regular) e. Interlobular connective tissue f• Intralobular connective tissue PLATE XX FfG- 38 PLATE XXI Fig. 39 Magramatio three dimensional view of the proventricular wall* a. FoveolaE gastricae b. Plica c. Trough d. Excretory duct. e. Cross section of tubules f. Long section of tubules g. Lobular gland h. Intralobular tubule i . Interlobular connective tissue Intralobular connective tissue PLATE XXI FIG. 3 9 -PLATE XXII Fig» 1*0» California murre. Proventriculus. HBedenhain's-Azan 60X a. Epithelium b« Lamina propria c. Muscularis mucosa d» Deep proventricular gland e. Submucosa f. Muscularis externa FIG- 40 PLATE m i l Fig. I 4 I . California murre. Proventricular excretory duct joining gastric crypt. Mallory's triple lijOX a. Gastric crypt b. Excretory duct c. Deep proventricular gland tubules d. Columnar epithelium Fig. 1*2. California murre. Proventricular gland tubules. Heiridenhain1s-azan 630X a. Tubule (cross section) b. Zymogen cel l c. Interlobular connective tissue d. Intralobular connective tissue PLATE XXItl PLATE XXIV Fig* k3» California murre. Proventriculus. Short Foot method for silver impregnation of reticulum. 60X a. Gastric crypt b. Lamina propria c. Muscularis mucosa ^ .d. Submucosa e. Blood vessels and nerves in the base of the gastric ridges. f. Muscularis externa g. Central collecting cavity of deep gland showing basement membrane. PLATE XXIV FfG/43 PLATE XXV Fig. lib* Screech owl. Preventriculus. Mallory's triple 6OX a. Epithelium b. Gastric crypt c. Tunica propria d. Deep proventricular gland e. Muscularis externa Fig« U5» Screech owl. Mucosa of proventriculus. Mallory's triple HiOX a. Epithelium b. Gastric crypt c. Tunica propria d. Excretory duct. e. Side branch of excretory duct. PLATE XXV FfG-45 PLATE XXVI Fig* U6m Screech owl. Longitudinal and transverse section of the deep gland tubules* Heindenhain1s-azan. a* Interlobular connective tissue b* Zymogan cell c* Cross section of tubule d. Longitudinal section of tubule Fig* U7* Screech owl* Nerve ganglion. lodian's silver stain* a* Tunica adventitia b* Circular layer of muscularis externa c* Nerve ganglion of the myenteric plexus PLATE XXVII Fig. U8. Peale's falcon, Proventriculus, Mallory's triple 60X a. Epithelium b* Tunica propria c. Gastric crypt Fig. U9» Peale's falcon* Gland tubules cross section. Verhoeff's elastic tissue stain 630X a* Zymogen cell b* Lumen c. Reticulum around iubule d. Blood ce l l PLATE XXV If FIG. 49 PLATE XXVTIT Fig« 50« Peale's falcon. Gastric mucosa. Mallory's triple UjOX a. Epithelium. b» Tunica propria c. Gland lobe d. Excretory duct e« Secretory tubules PLATE XXIX Fig* 51 • Sparrow hawk. Proventriculus. Heindenhain•s-azan 60X a* Epithelium b» Tunica propria c. Deep proventricular gland d. Muscularis externa e. Tunica adventitia PLATE XXX: Fig, 52, Sparrow Hawk, Proventriculus. Heindenhain's 1U0X a. Epithelium. b. Gastric crypt c. Gland lobe d. Excretory cavity Fig, 53, Sparrow Hawk. Proventricular gland tubules. Heindenhains'-azan, 630X a. Gland tubule b. Zymogen c e l l c. Intralobular connective tissue FIG. 52 h FIG-53 PLATE XXXI Drawings of the sphincters observed between the gizzard and the duodenum of the following birds: (Surface view, looking into the cavity of the duodenum.) Fig* 5U» Kingfisher. Sphincter. 15X a. Duodenal lumen b* Five bulbous muscular projections from the duodenal lumen* Fig* 55* California murre. Sphincter 15X a* Duodenal lumen b* Muscle band surrounding the opening of the duodenum. Fig* 56* Screech Owl. Sphincter a. Duodenal lumen. 15X b. Muscle surrounding the opening. Fig* 57 • Peale's falcon. Sphincter* a. Duodenal lumen b* Muscle surrounding the opening of the duodenum* c* Bulbous projections from the duodenal cavity* Fi&. 56 FIG. 57. PLATE XXXII Fig* 5>8» Kingfisher. Gizzard (thickest wall) Short Foot method for the silver impregnation of reticulum and Mallory's triple 60X a* Kerotinoid layer b. Tubular gizzard gland c. Muscularis mucosa d. Submucosa e. Muscularis externa f« Blood vessel FfG. 55 PLATE X f f l l l Fig, 59• Kingfisher gizzard. (Thinnest wall) Mallory's triple 60X. a* Keratinoid layer. b. Tubular gizzard gland c. Submucosa d. Muscularis externa e. Tunica adventitia f. Artery g. Vein* PLATE XXXIV Fig* 60* Kingfisher. Gizzard glands. Verhoeff's elastic tissue stain 63OX a* Gizzard gland b* Cuboidal epithelium c. Lumen of gland containing keratinoid secretion d. Lamina propria e. Muscularis mucosa f• Blood vessel FIG- 60 HATE XXXV Fig* 61 Kingfisher* Nerve fibre embedded in the smooth muscle of the gizzard. Mallory's triple 63OX a. Nerve fibre b* Smooth muscle c Fat PLATE X X X V c FIG-61 PLATE XXXVI Diagrammatic, longitudinal and transverse sections of the gizzard of the California murre, to show the gross arrangement of the muscle. (Dorsal side toward the top of the plate). Fig. 62. Longitudinal section of the gizzard a. Smooth muscle b. Glandular layer c. Keratin lining Fig. 63 Transverse section of the gizzard. a. Smooth muscle b. Glandular layer c. Keratin lining. PLRTE XXXVI. b. c. F I G . 6 2 . FIG. 6 3 . PLATE XXXVII Fig* 6lu California murre* Gizzard. Haematoxylin and eosin 60X* a* Keratinoid lining* b* Glandular layer c. Lamina propria d* Muscularis externa PLATE XXXVIII Fig* 6S>« California murre. Gizzard glands. Haematoxylin and eosin. 630X. A. Gizzard gland b. Cuboidal epithelium c. Lumen of gland containing keratinoid secretion d. Lanina propria e. Blood vessel f. Muscularis externa PLATE XX XV HI FIG 65 PLATE XXXIX Fig* 66 Screech Owl. Gizzard. Haematoxylin and eosin £OX a. Keratinoid layer b* Glandular layer c. Tunica propria d. Muscularis externa e. Tunica adventitia F IG. 6 6 PLATE XL Fig. 67 Screech owl. Transitional area between proventriculus and gizzard, Haematoxylin and eosin 63OX a. Epithelium b. Tunica propria c. Fibroblasts PLATE XL PLATE XLI Fig* 68* Screech Owl. Gizzard glands. Haematoxylin and eosin 630X a* Epithelium b. Keratinoid layer c. Capillary d» Neck of tubular gizzard gland e. Gizzard gland f• Colorless globules in the apical cells FfG. 6 8 PLATE XLII Fig. 69. Peales falcon gizzard. Haematoxylin and eosin 60X a. Keratinoid layer* b* Glandular layer c* Tunica propria d. Dense band of connective tissue enclosing groups of glands* e. Submucosa f. Muscularis externa PLATE XLtl FIG69 1 PLATE XLIII Fig* 70* Peale's falcon gizzard glands, Haematoxylin and eosin 630X a. Keratlnoid lining. b. Gizzard glands c. Apical cells of the gizzard ridges PLATE XLIII FIG. 70 PLATE XLIV Fig* 71 Sparrow Hawk. Gizzard. Mallory's Phosphotungstic Icid Haematoxylin 60X a. Keratinoid layer b. Glandular layer* c. Tunica propria d. Dense band of connective tissue e. Muscularis externa PLATE XL? Fig. 72 Sparrow hawk gizzard glands. Mallory's phosphot-ungstic acid haematoxylin 63OX a. Keratinoid lining b. Gizzard gland cell 

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