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Introductory studies on the development of the bones of the head in Clupea Pallasii Tomkinson, William 1940

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INTRODUCTORY STUDIES m THE DEVELOPMENT OE THE BONES OF THE HEAD IN CLUPSA PALLASII • bv W i l l i a m Tomkinson A Thesis submitted f o r the Degree of MASTER OE ARTS i n the Department of Z O O L O G Y B r i t i s h Columbia 1940 The U n i v e r s i t y of APRIL, ON THE DEVELOPMENT OP THE BONES OF THE HEAD IN THE PACIFIC HERRING, CLUPBA PALLASII. Table of Contents Acknowledgements.. . Page, i Introduction i i M a t e r i a l and Methods . . . . 1 Source of ma t e r i a l .. 1 T Q c i i m s • • • • • • < > • « » • • « « • • • • • « • JL i * o w t in »••••»••«•»»•••••••••••• 3 La r v a l m a t e r i a l used 4 Table of growth. 4a Part one, anatomy.;.... 5 Anatomical p l a t e s , I , I I , I I I , I V . 18 Part two, development.. 22 J_)x scussion» »»«*«»t«»«*f»»*«»»««* 37 Nomenclature. 4.2 nunsti^ j/ «•••»••«»••••••»••»•••••• 43 P l a t e s V, VI, V I I , V I I I , 44 Bib l i o g r a p h y . . . 49. ACKNOWLEDGEMENTS The w r i t e r i s indebted to Dr. W.A. Clemens f o r h i s so gracious and ready assistance i n the s e l e c t i o n of the problem, and together w i t h Dr. Hart and Mr. J.L. McHugh of h i s s t a f f at the P a c i f i c B i o l o g i c a l S t a t i o n , f o r the p r o v i s i o n of the l a r v a l m a t e r i a l . E s p e c i a l l y are thanks due to Dr. C. McLean Eraser who also a s s i s t e d with the s e l e c t i o n of the problem and who was a l l times h e l p f u l with suggestions and s o l i c i t o u s as to the progress of the work. at DEVELOPMENT OF THE BONES OF THE HEAD IN CLDPEA PAL*ASII INTRODUCTION The problem of the development of the bones of the head-of f i s h e s has i n t e r e s t e d authors f o r several years and has r e s u l t e d i n several theories of the o r i g i n of the head and i t s bones. In entering upon t h i s p a r t i c u l a r problem dealing with Clupea pal'asii the idea was not so much to i n v e s t i g a t e these,in t h i s r e l a t i o n , a s to open the subject up i n a p r e l i m i -nary way. Of i n t e r e s t currently i s the comparative anatomy of the North American P i l c h a r d , the Shad, and the P a c i f i c Herring, and out of t h i s was developed the subject i n v e s t i g a t e d i n the present paper. Whittaker ( l ) has anatomized the p i l c h a r d w i t h f a i r reference to the s k u l l , but of the other tv/o species I have been unable to f i n d any anatomical works. In connection wi t h the h e r r i n g I have had reference to Jordan's (2) volumes on the study of f i s h e s and to the above paper of -the p i l c h a r d by Whittaker. The. nomenclature used f o l l o w s that adopted by Jordan a f t e r Starks (3) who synonymized the bones of the skeleton of f i s h e s . By way of i n t r o d u c t i o n to the question of comparison of the three species a d e s c r i p t i o n of the bones of the head as found i n adult specimens i s presented here together w i t h i l l u s t r a t i o n s . This was ne c e s s a r i l y developed before any work 1. Whittaker, W.R., Anat. of N.A. P i l c h a r d , Thesis, 1932. 2. Jordan, D.S., Guide to Study of Pishes. 1905. pp 34-61. 3.Starks, E.C., The Synonymy of the P i s h Skeleton, 1901. could be done w i t h regard to the o s t e o l o g i c a l development. As to the l a t t e r question, the c o n d i t i o n of the s k u l l s a v a i l a b l e has been studied with regard to the degree of o s s i f i c a t i o n present,and to some extent considering the order of the appea* ranee and completion of the bones. L e f t open are questions to do w i t h more h i s t o l o g i c a l phases of the osteology of the s k u l l and towards these problem; t h i s i s hoped to c o n s t i t u t e an I n t r o d u c t i o n . DEVELOPMENT OF THE BONES OF THE HEAL IN CLUPEA PAlks.II MATERIAL and METHODS The l a r v a l m a t e r i a l used was a l l obtained from the P a c i f i c B i o l o g i c a l S t a t i o n at Departure Bay, B.C., through the courtesy of Dr. W.A. Clemens and various members of h i s s t a f f . This' m a t e r i a l was a l l stored i n a form a l i n f l u i d over a period of s e v e r a l years, which f a c t was believed to c o n s t i t u t e a d i f f i -c u l t y i n the way of any techniques to he a p p l i e d . Fortunately a l l of the m a t e r i a l was used without d i f f i c u l t y i n the prepara-t i o n f o r examinations. Mature specimens were obtained from the Vancouver dock-side o f f i c e of Edmunds and Walker, Fish-merchants. These were a l l taken from i c e w i t h i n a few hours of t h e i r d e l i v e r y from the f i s h boats at the dock. The l a r g e s t specimens were selected from the catches a v a i l a b l e at the time. A l l the observations of the s k e l e t a l elements were made on specimens prepared by i n toto s t a i n i n g methods. This method of examination has been used f o r some time i n studying many v a r i e d species of skeletons. Cumley, et a l ( l ) have pre-pared a good summary of the methods and t h e i r v a r i a t i o n s as a p p l i c a b l e to the preparation of material--for t h i s use. This summary i s a l i t t l e i n v o l v e d w i t h v a r i a t i o n s and I s h a l l only mention those basic p o i n t s which have been found to underlie most complete success. Both i n this,and with mammalian ma t e r i a l i t has been found (2) that the main idea i s to harden the t i s s u e completely i n the p r e l i m i n a r y treatment w i t h a l c o h o l , and then 1. Cumley et a l , S t a i n Technology,.14 (I), 1939, pp 7-12. 2. Tomkinson.W. Thesis 1936, Technique. -2-c l e a r with, a .potash s o l u t i o n of as low a concentration as w i l l carry out the r e a c t i o n r e a d i l y . B r i e f l y , the technique c o n s i s t s of hardening the s p e c i -mens i n a l c o h o l by running up from 25% to 95% strength; i n some cases the running up process may be eliminated and the ma t e r i a l placed d i r e c t l y i n 95% strength a l c o h o l . Several days or even weeks may p r o f i t a b l y be spent i n t h i s hardening process. At l e a s t one week i n the 95% a l c o h o l i s necessary f o r most m e t e r i a l and i n some cases a month may be required, upon completion of the hardening process the specimens are t r a n s f e r r e d to a KOH s o l u t i o n of about 4% strength u n t i l the bones are v i s i b l e through the c l e a r f l e s h , when the s o l u t i o n should be changed to 1%. In the case of l a r g e r specimens several changes of the potash s o l u t i o n may be required, changing whenever the f l u i d becomes d i s c o l o r e d * To the 1% bath a few drops of an aqueous or a l c o h o l i c s o l u t i o n of a l i z a r i n red are added u n t i l the f l u i d becomes l i g h t purple i n c o l o r . For small specimens the s t a i n may be added to the f i r s t potash bath, which w i l l render the ;r bones more r e a d i l y v i s i b l e at the completion of the c l e a r i n g . The amount of s t a i n used amounts to one part of s t a i n to 10,000 parts KOH. When s t a i n i n g i s complete the specimens are removed v. to a s o l u t i o n of 1% KOH i n 2Qjo g l y c e r i n e f o r a few days and then run up through g l y c e r i n e s o l u t i o n s to absolute g l y c e r o l . A few grains of thymol added to the g l y c e r o l w i l l prevent f o r -mation of mould. For immediate examination and d i s s e c t i o n a l c o h o l may be s u b s t i t u t e d f o r the g l y c e r i n e but i s not s a t i s -factory as a s t o r i n g medium. Some workers have reported a s p l i t --3-t i n g of the t i s s u e s when treated by t h i s potash method while the m a t e r i a l i s i n the g l y c e r i n e , but I have had mate r i a l i n t h i s c o n d i t i o n f o r over a year and i n only one case has the a c t i o n occured and then only a f t e r d i s s e c t i o n and repeated handlings and t r a n s f e r s from one container to others. The whole technique abbreviated i s of use i n preparing lar g e specimens f o r gross d i s s e c t i o n . In t h i s case the harden-ing process i s l e f t incomplete and the KOH i s used i n strong s o l u t i o n s with the s t a i n added immediately. Clea r i n g i s not ex-pected to take place but only a degree of maceration of the f l e s h so as to enable ready d i s s e c t i o n and r e v e l a t i o n of a l l osseous parts immediately. This was employed to prepare f i s h s k u l l s so as to study the a r t i c u l a t i o n s of the jaw bones. Examinations were a l l made wit a a binocular microscope and photographs of specimens were made on 35 mm. f i l m tnrough one of the eyepieces of such microscope. L i g h t f o r d i s s e c t i o n may be e i t h e r r e f l e c t e d or r e f r a c t e d , but f o r photography only r e f l e c t e d l i g n t from the substage mirror was p r a c t i c a b l e . The use of the type of f i l m employed i s not recommended?::for photo-micrography, but i n t h i s case the point i n consid e r a t i o n was the camera, to be ap p l i e d to the microscope, and p l a t e type machines were much too awkward and unmanageable compared to the camera using 35 mm. f i l m , e s p e c i a l l y w i t h regard to the bin o c u l a r microscope. Some idea of the rat e of growth at the time during which the specimens were taken may be determined from the accom-panying graph,taken, and modified w i t h regard to the present -4-rnaterial from G-wynn (1). This i s based on the f a c t of the time of hatching f o r the 1932 ma t e r i a l being March 19. Actual s i z e s of specimens at any time vary considerably, but the curve i s based on an average measure and i s intended merely to shew rate of growth during the time of tne appearance of the bones. LARVAL SPECIMENS EXAMINED; Date c o l l e c t e d ; Place c o l l e c t e d ; Length range; A p r i l 13 1932 Nanoose Bay 10 mm. to 12 mm. A p r i l 22 1932 Nanoose Bay 12 mm. to 14 mm. A p r i l 26 1932 Nanoose Bay 12 mm. to 14 mm. May 16 1932 Nanoose Bay 22 mm. to 23 mm. May 26 1932 Nanoose Bay 26 mm. to 27 mm. May 31 1932 Departure Bay 28 mm. to 39 mm. 1. Gwynn, A.M. Thesis 1938. -4a-Table of Growth. Length i n mm. March 19 H h br—i i o 12 weeks of Age. Chart to show the rate of growth during the period studied f o r the formation of the s k e l e t a l elements. (With m o d i f i c a t i o n s from Gwynn (1938)). OBSERVATIONS, Part one. The bones of the head: The order i n wnich these d e s c r i p t i o n s are given i s a r b i t r a r y , being based on that used by Jordan ( l ) , and used mainly because of i t s ready a d a p t a b i l i t y to the i l l u s t r a t i o n s . Nomenclature i s based on that synonymized by Starks (2). The S k u l l Proper : P l a t e s I I I , I V . The vomer,Pig. 1V, l i e s i n the a n t e r i o r part of the roof of the mouth. Dorsally a small horn turns up over the ros-t r a l c a r t i l a g e , i n t e r l o c k i n g over the body of the ethmoid. L a t e r a l l y two arms develop forming the a n t e r i o r t i p of the s k u l l , v e n t r a l l y a l a n c e - l i k e f l a t extension passes along a notch i n the parasphenoid, extending to belowtthe region of the o r b i t . At the a n t e r i o r end of t h i s part several teeth develop, borne i n a s w e l l i n g of the bone. The a n t e r i o r l a t e r a l arms form a r t i c u l a r surfaces f o r the t i p s of the m a x i l l a r i e s . The Ethmoid,Pigs. I I I , V t forms a mass p o s t e r o - d o r s a l l y to the vomer. A crest r i s e s to the mid-line of the dorsal sur-face of the head, l y i n g j u s t a n t e r i o r to the t i p s of the f r o n -t a l s . Arms p r o j e c t l a t e r a l l y beyond the l i m i t s of the vomer, and contacting the d o r s a l side of the t i p s of the p a l a t i n e bones. P o s t e r i o r l y the wings pass back beneath the f r o n t a l s to the o r b i t a l region. The P r e f r o n t a l s , P i g . I V , are paired bones forming the a n t e r i o r margin of the o r b i t . Wings pass down and forward de-marcating the o r b i t along i t s a n t e r i o r edge; these are p l a t e -1. Jordan, I.e. p. i i . 2. Starks, I.e. p. i i . l i k e . Medially the bodies of the bones pass v e n t r a l l y close to-gether, remaining embedded i n c a r t i l a g e . Dorsally wings pass beneath the f r o n t a l s along w i t h , and extending as f a r as, the d o r s a l wings of the ethmoid. Medial extensions j o i n w i t h the orbitosphenoid between the o r b i t s . F r o n t a l s , F i g . I l l , are l a r g e bones forming the dorsal surface of tne s k u l l from the ethmoid to the s u p r a - o c c i p i t a l bone. They form the e n t i r e d o r s a l cover of the cranium.Medially f o r most of t h e i r length one overlaps the other, rather than forming sutures. A n t e r i o r l y the t i p s are separated. P o s t e r i o r l y the bones f o r k sending arms l a t e r a l l y , and somewnat v e n t r a l l y , passing over the p t e r o t i c bone to i t s l a t e r a l edge. Tnis f o r k and the part remaining over the cranium form the superior tem-po r a l f o s s a . In passing over the sphehotic and p t e r o t i c bones the f r o n t a l fuses with them forming sutures. The P a r i e t a l s are small p a i r e d bones of i r r e g u l a r out-l i n e separated medially by the s u p r a - o c c i p i t a l bone, and l y i n g i n the angle formed by the f r o n t a l witn the s u p r a - o c c i p i t a l . They pass over the s u p r a - o c c i p i t a l s to form sutures with tne e p i o t i c s . A v e n t r a l extension forms the l i m i t of the e p i o t i c fossa. In mature specimens they are very hard to d i f f e r e n t i a t e from t h e i r neighbors witn whom tney are quite c l o s e l y j o i n e d . The S p h e n o t i c s , F i g s . I I I 7 v . form tne a n t e r o - l a t e r a l t i p s of the c r a n i a l s t r u c t u r e . D o r s a l l y they are obscured by trie f r o n t a l ; v e n t r a l l y they are bounded by the p t e r o t i c and p r o o t i c bones;medially they contact the a l i s p h e n o i d s . E p i o t i c s , F i g . V I , f o r m the extreme p o s t e r i o r t i p of the cranium. They' are small bones, rougialy t r i a n g u l a r i n o u t l i n e , with the angle somewhat rounded and bearing a small p r o j e c t i n g spine f o r a r t i c u l a t i o n of the post-temporal bone. Extensions of the s u p r a - o c c i p i t a l and p t e r o t i c bones fuse, along with the e x o c c i p i t a l s , to contact the e p i o t i c s . Within the curvature of the bone l i e s the v e r t i c a l s e m i - c i r c u l a r canal. The Supra-occipi t a l , F i g s . I l l , V , i s i n . two main p a r t s , one passing over the p o s t e r i o r part of the roof of the cranium, and the other l y i n g i n a v e r t i c a l plane as the p o s t e r i o r w a l l of the b r a i n case. The d o r s a l part separates the p a r i e t a l s , a n d l i e s beneath tne p o s t e r i o r part of the f r o n t a l s ; i t i s i n the form of three arms, the one medially, and the others l a t e r a l l y . The p o s t e r i o r v e r t i c a l part i s more heavily o s s i f i e d and l i e s between the e p i o t i c s , forming sutures a l s o to the e x o c c i p i t a l s along i t s v e n t r a l edges. At the angle where the two parts fuse a ridge forms, passing l a t e r a l l y across the s k u l l , while a small crest passes from t h i s f o r a short distance over the p o s t e r i o r part i n i t s m i d - l i n e . The P t e r o t i c s , F i g s . I I I T V I » are l a r g e , dense, i r r e g u l a r bones forming the p o s t e r i o r v e n t r a l surface of the cranium,and l i m i t i n g the s k u l l l a t e r a l l y and p o s t e r i o r l y . Sutures form w i t h the sphenotics, p r o o t i c s , e x o c c i p i t a l s , e p i o t i c s , and f r o n t a l s . L a t e r a l l y an i r r e g u l a r ridge forms the suspension of the hyomandibular, which acts as the main suspensorium of the systems about the mouth and operculum, and p o s t e r i o r l y along the d o r s a l surface a t h i n process develops to the other post-temporal a r t i c u l a t i o n . Opis'thotics , i f i g . IV, are t i n y , almost c h i p - l i k e , bones, p r a c t i c a l l y i n d i s c e r n i b l e i n mature s k u l l s without thorough d i s s e c t i o n . They l i e v e n t r a l to the suture of the e x o c c i p i t a l , p r o o t i c , and. p t e r o t i c bones. A small s p i n e - l i k e process passes p o s t e r i o r l y f o r r e c e p t i o n of the post-temporal's v e n t r a l arm. S x o c c i p i t a l s , F i g . I l l , I V , v l , are large i r r e g u l a r bones, meeting medially to form, w i t h the s u p r a - o c c i p i t a l , the poster-i o r surface of the s k u l l . Also medially they fuse along the mid-dorsal edge of the b a s i - o c c i p i t a l , so as to form the f o r a -men magnum. A p r o j e c t i o n develops on the p o s t e r i o r p l a t e s pass-i n g to the e p i o t i c bones. L a t e r a l l y i r r e g u l a r wings fuse to the p t e r o t i c s and p r o o t i c s , contacting also the o p i s t a o t i c s . Tney form, wi t h the p r o o t i c s , most of the f l o o r of the brain case, and,with the s u p r a - o c c i p i t a l , t n e p o s t e r i o r w a l l of the c a v i t y . The Bas'occipi t a l i s a long centrum? shaped bone l y i n g under the foramen magnum i n the channel formed by the e x o c c i p i -t a l s . A n t e r i o r l y i t meets the medial f u s i o n of the p r o o t i c s , and p o s t e r i o r l y i t has a concave a r t i c u l a t i o n f o r the f i r s t vertebra. V e n t r a l l y two l o n g i t u d i n a l wings are developed,form-i n g , with the parasphenoid, the p o s t e r i o r p a r t of the myodome. The Parasphenoid,i<'igs.IV-VI, l i e s along the v e n t r a l edge of the s k u l l from the a n t e r i o r part of the vomer to the p o s t e r i o r t i p of the b a s i o c c i p i t a l . .below the o r b i t a l region the bone i s a narrow, r o d - l i k e , s t r u c t u r e , somewhat compressed d o r s o - v e n t r a l l y . Under the a n t e r i o r edge of the cranium the bone sends small d o r s a l extensions to the a n t e r i o r medial ven-t r a l corners of the p r o o t i c bones. Erom here two non-divergent wings pass p o s t e r i o r l y , forming .the myodome together with the v e n t r a l wings of the p r o o t i c s and b a s i o c c i p i t a l bone,(Fig.IV). The Prootics,Fig.IV,V, form the greater part of the ve n t r a l surface of the br a i n case. They contain the o t i c cap-sul e . They u n i t e medially along the myodome, f u s i n g w i t h the b a s i o c c i p i t a l and sending out v e n t r a l wings s i m i l a r to those of the b a s i o c c i p i t a l . Sutures form l a t e r a l l y to the p t e r o t i c , p o s t e r i o r l y to the p t e r o t i e s , e x o c c i p i t a l s , and a p i s t h o t i c s , a n t e r i o r l y to the sphenotics, a l i s p h e n o i d s , basisphenoid, and parasphenoid. The a n t e r i o r half, of the f l o o r of the b r a i n case i s made up of these two bones. The Alisphenoids,Pig.IV,V, are two somewhat square bones l y i n g i n the postero-dorsal quadrant of the o r b i t between the orbitosphenoid and the p r o o t i c bones. Medially a lar g e f o r -amen separates the two, but they fuse a n t e r i o r l y to,the o r b i t o -sphenOid,posteriorly to the basisphenoid, the p r o o t i c s and the sphenotics. Along t h e i r d o r s a l edge they contact tne f r o n t a l at i t s e c t a l rim behind the o r b i t s . They c o n s t i t u t e the a n t e r i o r w a l l of the b r a i n case, or,with the p r o o t i c s , t h e f l o o r . The Basi sphenoid i s a s i n g l e bone of somewhat H shape. I t l i e s between the alisphenoids and across the a n t e r i o r edge of the p r o o t i c s at the a n t e r i o r end of the myodome. A small medial p r o j e c t i o n passes v e n t r a l l y to d i v i d e the a n t e r i o r mouth of the myodome i n t o two p a r t s . In the adul t the s i m i l a r i t y to' the l e t t e r H i s reduced by broadening of the cross-bar, but i n the l a r v a l stages the bar i s r e l a t i v e l y narrow. The Orbitosphenoid i s a s i n g l e bone forming the f l o o r -10-of the b r a i n case i n the region of the f o r e - b r a i n . This may be formed by the f u s i o n of two bones as the l i t e r a t u r e i n d i c a t e s , but at no time i n the f i s h studied was t h i s c o n d i t i o n i n d i c a t e d P o s t e r i o r l y i t i s q u i t e wide f u s i n g to the a l i s p h e n o i d s . This width f a l l s o f f passing a n t e r i o r l y so that the whole o u t l i n e i s s i m i l a r to the prow of a ship w i t h a bow-sprit or f i g u r e -head attached.At about the mid-point of the wide s t r u c t u r e and approximately n a i f way along the e n t i r e length of the bone an arm passes o f f m e d i a l l y , continuing a n t e r i o r l y to contact the p r e f r o n t a l s . This arm i s f l a t t e n e d l a t e r a l l y and forms a blade separating the o r b i t s . .The wider l a t e r a l parts of the bone pass along to almost contact the f r o n t a l s . This, with the a l i -sphenoids , and prefrontals,forms the roof and p o s t e r i o r and a n t e r i o r w a l l s of the the o r b i t s . *' These bones make up the s k u l l or cranium w i t h i t s b r a i n c a v i t y , o r b i t s , and auditory and o l f a c t o r y regions.Some of the bones are of a membranous character\ otners are of a more deep nature.apparently preformed i n c a r t i l a g e . Those bones which are d e f i n i t e l y of a c a r t i l a g i n o u s nature l i e i n the region of the chondrocranium, but some of the bones which are of the mem-branous type a l s o are included i n the l i t e r a t u r e i n the l i s t s of bones forming i n the region of the chondrocranium and there-fore preformed of c a r t i l a g e . Because of t h i s degree of uncer-t a i n t y , the r e g i o n a l system of l i s t i n g tae bones was omitted and as before mentioned the a r b i t r a r y system was adopted. The Suspensory System: The Hyomandibular i s the p r i n c i p l e suspensory bone f o r - l i -the systems of bones about the mouth and opercular region. D o r s a l l y i t i s quite a heavy bone, connecting to the l a t e r a l ridge of the p t e r o t i c bone. In t h i s region i t i s massive, but tapers i r r e g u l a r l y to the point at which i t connects with the symplectic and i n t e r h y a l bones, wings form along the a n t e r i o r edge of the tapering body, forming w i t h the metapterygoid bone some of the roof of the mouth. A small p r o j e c t i o n develops at the more do r s a l end of the bone on the p o s t e r i o r edge f o r the attachment of the opercle to which are attached the otaer mem-bers of the operculum.(See F i g . I I ) The S y m p l e c t i c , j i g . I I , i s a long c y l i n d r i c a l bone con-necting at the v e n t r a l t i p of the hyomandibular and passing i n t o a groove i n the quadrate to complete the suspensory system. This i s one of the very few r e g u l a r l y shaped bones of a l l those i n the head, having a s i m i l a r shape to the long bones of limbs of t e r r e s t r i a l tetrapods. I t s f u n c t i o n as a suspensory bons i s most apparent i n the l a r v a l stages when the metapterygoid i s incomplete and no bone, other than the symplectic, connects the hyomandibular to the bones of the lower jaw, or roof of the u> outn The Bones of the Koof of the Mouth: F i g . I I . The Q.uadrate bone i s included here because i t i s i n close union w i t h these bones, although i t i s more of a suspen-sory bone. This i s a t r i a n g u l a r bone bearing at i t s antero-v e n t r a l apex the a r t i c u l a t i o n f o r the lower jaw. Along i t s v e n t r a l edge a narrow c o n i c a l socket i s formed f o r the recep-t i o n of the symplectic. A n t e r i o r l y i t f i t s c l o s e l y i n t o a groove i n the pterygoid bone, wiaile along i t s postero-dorsal -12-edge i t contacts the metapterygoid. The P t e r y g o i d , F i g . I I , a s l i m bone bent i n t o an angle of about 100°, l y i n g along the a n t e r i o r edge of the quadrate,forms the suspension and connection of the roof of the mouth to the r e s t of the bones of the chain. At i t s a n t e r i o r t i p i t bears the p a l a t i n e bone, and along i t s dorsal edge i t supports the mesopterygoid. A rather heavy c a r t i l a g e l i e s i n the d o r s a l groove and holds to the antero-dorsal apex of the quadrate, keeping these bones i n p o s i t i o n . The P a l a t i n e , F i g . I I , i s a small bone borne at the t i p of the pterygoid. A n t e r i o r l y , t h i s bone i s massive and has an a r t i c u l a r surface f o r the m a x i l l a r y . I t l i e s quite close to, and j u s t beneath the l a t e r a l arms of the ethmoid bone. This a n t e r i o r t i p i s quite massive but the p o s t e r i o r part which con-tac t s the pterygoid i s more membranous i n character. The Mesopterygoid,Figs.I,II,is a somewhat p l a t e - l i k e bone forming a l a r g e part of the roof of the mouth. I t i s borne mainly i n the groove of the pterygoid but a l s o contacts the meta-pterygoid bone p o s t e r i o r l y . The M e t a p t e r y g o i d , F i g . I I , i s an i r r e g u l a r l y shaped membranous bone, a t t a c n i n g to the mesopterygoid and the hyo-mandibular bones, and l y i n g i n the roof of the mouth. The Opercular.system: F i g s . I , I I . The P r e o p e r c l e , F i g s . I , I I , i s a l a r g e p l a t e - l i k e angular bone w i t h one arn l y i n g along the most v e n t r a l edge of the quad-rate bone. This arm forms one side of an angle of nearly 120°, the other arm proceeding d o r s a l l y along the l i n e of the poster--13-i o r margin of the hyomandibular and extending almost to the a r t i c u l a t i o n of t h i s bone w i t h the p t e r o t i c . The bone widens out considerably at the angle, so that the external angle i s more-nearly 90°. The arms are quite wide p l a t e s o v e r l y i n g the opercle and the other bones of the system. O p e r c l e , F i g s . 1 , I I , i s the name given to the large bone forming the main part of the operculum. This bone attaches to the hyomandibular near i t s d o r s a l extremity,and l i e s with i t s a n t e r i o r edge under the p o s t e r i o r border of the preopercle.The shape of the operculum i s l a r g e l y determined by the opercle. The S u b o p e r c l e , F i g s . I , I I , i s s i t u a t e d v e n t r a i l j to the, opercle, f i t t i n g quite c l o s e l y to i t s border. I t s outer edge continues the curvature of the opercle forming the angle of the whole operculum. The I n t e r o p e r c l e , F i g s . I , I I , i s s i t u a t e d along and under the v e n t r a l edge of the preopercle, and j u s t a n t e r i o r to the subopercle. This i s a long p l a t e - l i k e bone somewaat conf u s i b l e w i t h the l a s t of the branchiostegals over which i t l i e s * The Hyoid Dystem: F i g . I I . The I n t e r h y a l i s a small tubular bone a r t i c u l a t i n g close to the symplectic with the hyomandibular. I t forms the suspensory f o r the hyoid system. Passing i n a somewnat postero-v e n t r a l d i r e c t i o n i t connects at the p o s t e r i o r t i p of the e p i -hyal bone. The E p i h y a l i s roughly shaped as a r i g h t - t r i a n g l e with the r i g h t angle at the a n t e r i o r v e n t r a l p o s i t i o n . The i n t e r h y a l connects to the p o s t e r i o r angle,while the ceratohyal l i e s close -14-to the a n t e r i o r border. The Ceratohyal i s a large rectangular bone formed of two parts separating along the long c e n t r a l a x i s . V e n t r a l l y small notches form a r t i c u l a t i o n s f o r the branchiostegals. A n t e r i o r l y the basihyals contact the ceratohyal. The Basihyals-are two i r r e g u l a r massive bones,one moun-ted at the end of the ceratohyal, and the other upon the dorsal surface of the f i r s t . From the d o r s a l p a i r the glossohyal pas-ses a n t e r i o r l y and the urohyal p o s t e r i o r l y . The G-lossohyal i s a s i n g l e s l i m bone s i t u a t e d i n the t i p of the tongue passing from the b a s i h y a l s . Small teeth are borne on the d o r s a l surface of t h i s bone. The Urohyal i s a s i n g l e sword shaped bone with the blade d i r e c t e d p o s t e r i o r l y along the mid-line beneath the ton-gue. A n t e r i o r l y the bone i s narrow, but fo r k s to a r t i c u l a t e on the i n s i d e surfaces of the b a s i h y a l s . The Branchiostegals are s l i m curved bones borne along the v e n t r a l edges of the ceratohyals and epihyalobDnesicEiveiit; p a i r s are on the ceratohyals and three p a i r s along the epihyalo They support a membrane which protects the v e n t r a l side of the tongue. The f i r s t f i v e p a i r s are s l i m and are borne i n a r t i c u -l a r notches, but the l a s t three p a i r s are f l a t t e r and not borne i n a r t i c u l a t i o n s , but .seem to be a p p l i e d f l a t at t h e i r a n t e r i o r t i p s . These three become successively l a r g e r , u n t i l the l a s t i s comparable w i t h the subopercle. The Lower Jaw: F i g s . I , I I . The A n g u l a r , F i g . I I , i s a small bone at the p o s t e r i o r t i p of the a r t i c u l a r , j u s t below the point of a r t i c u l a t i o n with the quadrate bone at i t s a n t e r i o r v e n t r a l t i p . The a r t i c u l a r , g i g . I I , i s a t r i a n g l e shaped bone wit h two sides quite h e a v i l y o s s i f i e d about a maaibranous body. The heavy developments are along the v e n t r a l and p o s t e r i o r borders from the p o s t e r i o r a r t i c u l a r t i p , which i s heavy and massive i n appearance. The v e n t r a l edge l i e s along the i n s i d e of the dentary to almost the t i p of that bone. The Dentary , Jj'igs. I , I I , i s s i m i l a r to the a r t i c u l a r i n i t s general s t r u c t u r e , w i t h two sides w e l l o s s i f i e d and a rhom-boid shaped ,more membranous,inner part. The v e n t r a l edge passes along beneath the a r t i c u l a r , q u i t e c l o s e l y applied to i t , a l m o s t to the a r t i c u l a t i o n p o i n t . Along the a n t e r i o r border a curved t h i c k e n i n g passes from the t i p d o r s a l l y , and p o s t e r i o r l y , shaping the mouth. These two bones are assembled so that t h e i r d o r s a l wings meet with the p o s t e r i o r edge of the dentary o v e r l y i n g the a n t e r i o r edge of the a r t i c u l a r . These wings form the l a t e r a l w a l l s of the mouth and cheeks.(See F i g , I I . } The Upper Jaw: F i g s . I , I I . The P r e m a x i l l a r y i s a small, somewhat f l a t t e n e d , s t r u c -ture curved medially over the vomer, and l a t e r a l l y along the a n t e r i o r edge of the m a x i l l a r y . There are no teeth, and no a r t i c u l a t i n g surfaces i n t x i i s species. The M a x i l l a r y i s a l a r g e bone c o n s i s t i n g of a some-what c u r v e d , p l a t e - l i k e body, bearing small t e e t h along i t s ven-t r a l edge and a thin,stout,curved p o r t i o n a n t e r i o r l y , w h i c h turns medially so* that the t i p s of the r i g h t and l e f t members almost contact medially. A r t i c u l a t i o n s develop at tne t i p s to the vomer, and, a short distance from the t i p , to the base of the p a l a t i n e bone. The Admaxillary, or supermaxillary i s a f l a t t e n e d bone expanded p o s t e r i o r l y a n d l y i n g along the d o r s a l margin of the m a x i l l a r y . The p o s t e r i o r widened blade overlaps the p o s t e r i o r part of the m a x i l l a r y blade. A second,smaller,long,thin,narrow bone l i e s immediately on the m a x i l l a r y , and covered by the f i r s t mentioned admaxillary. The O r b i t a l iiones: i l g I. These are a chain of small membranous bones s i t u a t e d i n the c i r c u r n o r b i t a l part of the head. They form a r i n g about the eye, i n t h i s species passing completely around i t , both above and below, i n f r o n t of, and behind the eye. The S u b o r b i t a l chain i s made up of three/bones l y i n g i n the l a t e r a l p o s t e r i o r part of the eye region,, The p r i n c i p a l member i s a large bone derived from two or more centres j u s t below the eye. A n t e r i o r l y , i t does not quite reach to the pre-o r b i t a l , but p o s t e r i o t l y i t i s i n close union with the other two parts of the chain which pass up the p o s t e r i o r edge of the o r b i t . A l l three of these bones bear a ridge running j u s t away from, but p a r a l l e l to,- the edge of the o r b i t . P o s t e r i o r l y these bones come quite close to the preopercle. The S u p r a o r b i t a l bone l i e s i n the a n t e r i o r d o r s a l quad-rant of the eye region, between the f r o n t a l bone and the edge of the o t b i t . I t i s long,and somewhat t r i a n g u l a r i n shape. -17-In the P r e o r b l t a l region are two bones, one a l a r g e f l a t s t r u c t u r e and the other a smaller t r i a n g u l a r bone. The l a r g e r of these overlaps on the ma x i l l a r y group and f i l l s most of the space between the eye and the m a x i l l a r i e s . I t does not quite extend p o s t e r i o r l y as f a r as the s u b o r b i t a l s but i s c l o s e l y con-nected w i t h the other of these two bones and through i t to the s u p r a o r b i t a l . The smaller bone passes from the t i p of the supra-o r b i t a l to the t i p of tne p r e o r b i t a l mentioned above. I t f i l l s a good part of the area not covered by the other bones i n t h i s region. Lying i n l i n e w i t h the f r o n t a l s and at the a n t e r i o r t i p of that bone j u s t medial to the p r e o r b i t a l s i s the Nasal bone. This i s on the medial edge of the n a r i s . In a l l cases except where a c t u a l l y noted otherwise the above bones, i . e . a l l those since the s k u l l was completed, are d u p l i c a t e d on the other side of the head, whenever a single bone was noted as such there was only one such, but whenever the f a c t of p a i r i n g was noted there a c t u a l l y was meant that i n the e n t i r e head there are four such bones. PLATS I -Subopercle Opercle Interopercle Preopercle Sranchioste Suborbi t a l s Parasphenoi Ltesopterygo Oi b i t - •* Orbi tospiien Supraorbi t a l P r e f r o n t a l ^ A d m a x i l l a r i es Preorbi t a l s Nasal — A r t i c u l a r M a x i l l \ r P r e rnaluTl a r j Dentary L a t e r a l view of tne nead to snow dermal bones and systems i n s i t u . -18-PLATE I I Subopercle — Interopercle-Opercle Preopercle Hy omandibular Symplectic Metapteryg Quadrate Mesopterygoid Pterygoid P a l a t i n e A d m a x i l l a r i e s M a x i l l a r y > Interhyal Epinyal Branchiostegals Ceratonyal Angular""1 A r t i c u l a r Dentary I Basihyals Hypobranchial Glossohyal Showing bones of the nead otner than i n the cranium , p a r t l y d i ssected. -19-PLATE I I I -Vomer -Teeth-"Ethmoid" -Nasal P r e f r o n t a l . Parasphenoid — Fr o n t a l Orbitosphenoid-A l i sphenoid^ Sphenotic P r o o t i c — P a r i e t a l P t e r o t i c S u p r a o c c i p i t a l Opi s t n o t i c — -Ex o c c i p i t a l E p i o t i c -B a s i o c c i p i t a l -Dorsal view Foramen Magnum Parasphenoid Tips-wings of Parasphenoid have been omitted i n v e n t r a l view to show the B a s i o c c i p i t a l . Ventral View -20-PLATE I I I I F r o n t a l Alisphenoid Orbitosphenoig Nasal Ethmoid Vomer P r e f r o n t a l Supraoccipi t a l P a r i e t a l E p i o t i c F r o n t a l P t e r o t i c E x o c c i p i t a l JL^Sphenotic P r o o t i c -Basisphenoid B a s i o c c i p i t a l -Parasphenoid L a t e r a l View / S u p r a o c c i p i t a l E p i o t i c E xoccipi t a l P t e r o t i c Foramen Magnum Opi s t h o t i c t i p B a s i o c c i p i t a l Parasphenoid Myodome P o s t e r i o r View -21--22- , OBSERVATIONS, Part two. The f o l l o w i n g i s a d e s c r i p t i o n of the bone develop-ment based on the order of the appearance of the separate bones. Each bone i s described as i t appears and i s followed through i t s subsequent development as observed. The e a r l i e s t o s s i f i c a t i o n of the bones of the h e r r i n g i s found i n specimens of 14 mm. length. In the head there are the dentaries and m a x i l l a r i e s ; elsewhere there i s the c l a v i c l e . The dentaries and m a x i l l a r i e s appear as curved rods l y i n g i n the region of the heaviest development of the mature bones, /it t h i s stage they are l i t t l e more than i n d i c a t o r s of the p o s i t i o n to be occupied by the bones they represent. The c l a v i c l e s are s i m i l a r at t h i s stage. The m a x i l l a r y bone develops f i r s t along i t s v e n t r a l edge and at the a n t e r i o r curvature, so that the general an-t e r i o r o u t l i n e becomes ascertained before the p o s t e r i o r wing i s o u t l i n e d . Erom the c o n d i t i o n noted i n the 14 mm. specimens the a n t e r i o r t i p develops continuously, u n t i l , i n the 26 mm. condition,the r e l a t i v e p o s i t i o n s of the p r e m a x i l l a r i e s and m a x i l l a r i e s are apparent. At 28 mm. the general o u t l i n e of the bone i s quite d e f i n i t e i n i t s d o r s a l and p o s t e r i o r regions. A t 30 mm. the a r t i c u l a r surfaces at the medial t i p s are beginning to be i n d i c a t e d , and i n the l a r g e s t specimens observed, 39 mm., the bones are almost complete except f o r development of a c t u a l ,. a r t i c u l a t i o n s . A t 39 mm. the r e l a t i o n of trie p a l a t i n e bone to the m a x i l l a r y i s almost a completed a r t i c u l a t i o n as i n the a d u l t . The 'dentary bone, as i t appeared i n the 14 mm. stage, consisted of a t h i n curved rod. Development continues at a f a i r l y good r a t e , showing i n the 22 mm. stage with considerable a n t e r i o r and v e n t r a l development, as w e l l as the appearance of o s s i f i c a t i o n along the antero-dorsal edge, p o s t e r i o r l y l i t t l e development has continued, i n tne 26 mm. specimens almost a complete o u t l i n e i s apparent with considerable depth of o s s i f i -c a t i o n along the v e n t r a l and a n t e r i o r parts.' Medially the t i p s are quite close together, but are not completely formed. By 28 mm. the general o u t l i n e i s completely developed, l a c k i n g s t r u c t u r e only i n the depth of the a n t e r i o r curvature and t i p s . A n t e r i o r l y development concerns the dorso-ventral depth of the t i p . In the 39 mm. specimens the bone has quite complete f o r -mation,both by i t s e l f , a n d i n conjunction w i t h the angular bone. In the 22 mm. specimens several bones make t h e i r f i r s t appearances. One of these i s the premaxillary which appears as a small curved bar r e v e a l i n g no other data than the p o s i t i o n of the bones. Up to the specimens of 27 mm. l e n g t h the develop-ment i s i n d i c a t e d i n the breadth of the bone and general s i z e . Some i n d i c a t i o n of the f i n a l shape i s i n d i c a t e d i n the specimen of 28 mm. length, when the e c t a l e x t r e m i t i e s can d e f i n i t e l y be sai d to i n d i c a t e , the f i n a l curved form of the bone as i t l i e s i n the upper jaw. Medially the bones are s t i l l f a i r l y free of a r t i c u l a t i o n s . In the 39 mm. specimens f i n a l form i s l a c k i n g only i n the medial development, and i n reference to the method of a r t i c u l a t i o n . i n the same region,the a d m a x i l l a r j appears as an o s s i f i c a t i o n ? i n the shape of a bar along i t s mid-line i n 22 mm. specimens. .Development continues as regards the length of t h i s bar, and to some extent the p o s t e r i o r blade has appeared i n 27mm In specimens greater than 28 mm. long, the f u l l form and posi t i o n of t h i s bone i s apparent. The smaller admaxillary.which i s s i t u a t e d along the d o r s a l edge of the m a x i l l a r y , was not appar-ent u n t i l 39 mm. of length, but a t t h i s stage was located as an o s s i f i e d p l a t e s i m i l a r i n o u t l i n e to the adu l t form, and of s i m i l a r r e l a t i v e development to other members of the Sj stem. At 22 mm. a l s o , the a r t i c u l a r bone of the lower jaw appears as an o s s i f i c a t i o n along i t s v e n t r a l edge, possibly the o s s i f i c a t i o n of MeckelSs C a r t i l a g e . Some i n d i c a t i o n of the postero-dorsal edge i s present at t h i s stage. By 26 mm. the o o u t l i n e i s f a i r l y complete,but only f a i n t l y , i n that part of the wing which l i e s w i t h i n the dentary bone. At 28 mm. the low-er jaw s t r u c t u r e formed by the dentary and a r t i c u l a r i s prac-t i c a l l y completed. At 24 mm. there seems to be a small centre i n the region of the angular, which,although deeply o s s i f i e d , i s fused with the a r t i c u l a r . No f u r t h e r i n d i c a t i o n of a centre f o r the angular appeared than t a i s . The quadrate bone also appears with an o s s i f i c a t i o n along i t s v e n t r a l edge at 22 mm. This bar f i t s c l o s e l y to the a r t i c u l a r at i t s a n t e r i o r end. Development continues u n t i l at 28 mm. the f u l l o u t l i n e of the bone i s apparent, except i n a small part of the postero-dorsal edge. At 39 mm. r e l a t i v e l y l i g h t o s s i f i c a t i o n i s apparent i n the region of the j u n c t i o n w i t h the metapterygoid bone, -25-The members of the operculum,begin to appear at 22 mm. of length. The opercular bone f i r s t o s s i f i e s i n the,region of i t s p oint of a r t i c u l a t i o n w i t h the hyomandibular, with a small fan-shaped centre spreading out'over about one-fourth of the p o t e n t i a l shape of the bone. Development proceeds u n t i l by 28 mm. the bone i s p r a c t i c a l l y completely i n d i c a t e d and i n i t s mature p o s i t i o n r e l a t i v e to the neighboring bones, as i n d i c a t e d by. overlappings. At 39 mm. the d i s t a l edges are s t i l l somewhat l i g h t l y o s s i f i e d , i n d i c a t i n g that development i s not yet f u l l y complete. The preopercular> bone appears f i r s t as a thin,angular o s s i f i c a t i o n , l y i n g along the inner angle of the bone. Sub-sequent appearance of the greater part of the bone comes slowly, appearing i n the v e n t r a l part by 26 mm., and passing to the p o s t e r i o r part by 28 mm. At 30 mm. some of the d o r s a l t i p re-quires to be developed, but by 39 mm. complete development appears to be present. At 22 mm. a l i g h t o s s i f i c a t i o n appears i n the region of the i n t e r o p e r c u l a r bone, i t s development being s t e a d i l y con-tinued u n t i l , a t 30 mm..almost complete s t r u c t u r e has been reach-ed. By 39 mm. the bone seems to be completely formed. In a l l of the members of the opercular system at 39 mm. the d i s t a l edges are t h i n l y developed, so as to i n d i c a t e incomplete o s s i f i c a t i o n , although the general shapes are quite complete. In the s k u l l proper the e a r l i e s t formation of bone i s seen i n the parasphenoid bone, which i s present as a w e l l o s s i -f i e d bar below the o r b i t a l region i n 22 mm. specimens. At t h i s -26-time trie a n t e r i o r bar beneath the o r b i t and some i n d i c a t i o n of the f o r k i n g below the o r b i t i s present. The f u l l length i s determined i n the 24 mm. specimens when the bone passes from the vomerine region to the b a s i - o c c i p i t a l bone. The wings be-neath the cranium a t t a i n t h e i r f u l l s i z e and shape by 53 mm. of length, and i n tne 39 mm. specimen tne bone i s quite l i k e i t s mature form. In the region of the f o r k i n g beneath the p r o o t i c bones the parasphenoid i s of somewhat n e t - l i k e structure at the 39 mm, stage. The o t i c capsule i s f i r s t d e f i n i t e l y o s s i f i e d at 22 mm. when i r r e g u l a r o s s i f i e d centres appear i n the surface of the capsule proper. In 28 mm. specimens some of the body of the p r o o t i c bone begins to be indicated,and by 30 mm. the o t i c cap-sule has become embedded i n the p r o o t i c bone s t r u c t u r e . In the 39 mm. stage the p r o o t i c i s deeply o s s i f i e d i n most of i t s ma-ture shape, but i s incomplete on a l l edges w i t h wide f i s s u r e s to a l l the neighboring bones. Medially and p o s t e r i o r l y , especia-l l y , considerable development i s required to reach the adult form completely. Another of the early appearing s k u l l bones i s the f r o n -t a l bone, which developed f i r s t along i t s angular edges about the rim of the cranium and over the o t i c region, and along the ridge over the o r b i t a l region. At 22 mm. the o s s i f i c a t i o n i n the outer margins over the cranium appears. At 24 mm. the previous parts have strengthened, and to some extent passed a l i t t l e a n t e r i o r l y over the o r b i t . Just over the a n t e r i o r w a l l of the brain-case small bars pass medially from the l a t e r a l -27-. ridges previously noted. In the 27 mm. specimens development i s i n degree over the 24 mm. pa r t s , w i t h no new structures apparent, At 28 mm. some i n d i c a t i o n of development of the sup r a - c r a n i a l membrane appears, but only l i g h t l y . The framework over the cra-nium and l a t e r a l l y over the o t i c region i s nearly eomplete. In the 39 mm. specimen the general o u t l i n e of the bone i s seen, but i s incomplete as regards depth of o s s i f i c a t i o n . S t a r t i n g i n 22 mm. specimens i n d e f i n i t e o s s i f i c a t i o n appears i n the roof of the mouth, which may be the mesoptery-goid, but at t h i s stage seems somewhat cursory and not s u f f i -c i e n t to be recorded as a d e f i n i t e o s s i f i c a t i o n . In the 26 mm. specimens the l a s t of the opercular bones f i r s t appears. This, the suboperculum, appears as a crescent-shaped p l a t e . Development continues u n t i l , i n 28 mm. specimens, the complete s t r u c t u r e seems to be present, subject to the pre v i o u s l y mentioned l i m i t a t i o n that d i s t a l growth i s s t i l l not f u l l y completed. .The pt e r y g o i d appears at 26 mm. as an angle of o s s i f i -c a t i o n , showing the p o s i t i o n and shape of the bone. Growth proceeds mostly i n the groove i n t o which the quadrate and pala-t i n e bones f i t , and at 30 mm. the str u c t u r e seem to be complete g e n e r a l l y . The mesopterygoid snows as a l i g h t l y o s s i f i e d p l a t e i n , the roof of the mouth at 26 mm., being p r a c t i c a l l y complete i n s i z e and general shape by 28 mm. At 39 mm. the str u c t u r e i s complete except as regards i t s l i m i t i n g edges where i t meets surrounding bones. -28-At.26 mm. the members of the hyoid system commence to appear. At t h i s tiime the cerato-hyal and b a s i - h y a l bones have traces of o s s i f i c a t i o n , but hardly of s u f f i c i e n t development to be described as centres. They may, however, be s a i d to have commenced o s s i f i c a t i o n at t h i s stage. In the next stage., 27 mm., the cerato-hyal has a centre somewhat l i k e a diaphysis l y i n g along the lower n a i f of the bone. At 28 mm. t h i s centre has i n -creased i n s i z e , but has not included much more of the bone. The v e n t r a l edge with the a r t i c u l a t i o n s f o r branchiostegals i s not yet o s s i f i e d , but seems to be demarcated as i n c a r t i l a g e . By 30 mm. the v e n t r a l part has become f a i r l y w e l l developed except f o r the edge which bears the branchiostegals, which re-mains a smooth curve. D o r s a l l y , a l i t t l e i n d e f i n i t e development has begun. At 33 mm. the ends of the, f i r s t mass develop d o r s a l -l y , curving back over the centre present, and enclosing a new mass of o s s i f i c a t i o n separated widely from most of the f i r s t centre. The 39 mm. specimen shows the v e n t r a l h a l f deeply o s s i -f i e d , and bearing notches along i t s edge f o r the reception of branchiostegal t i p s . The dorsal s e c t i o n i s showing, but not so deeply as the v e n t r a l p a r t . The b a s i h y a l s commence at 26 mm. with an i r r e g u l a r l y o s s i f i e d mass i n the region of the v e n t r a l parts, which develop _ a l i t t l e by way of s i z e i n 27 mm. specimens. In the 28 mm. stages there i s a massive centre quite dense and i r r e g u l a r , showing some of the mature shape, and i n d i c a t i n g a r t i c u l a r surfaces. The 30 mm. specimens show four i r r e g u l a r centres of o s s i f i c a t i o n , the smaller d o r s a l p a i r having j u s t appeared, separated considerably and with the v e n t r a l p a i r close to the ceratohyal. In the cranium proper several new s t r u c t u r e s are found i n the 26 mm. h e r r i n g . Of these, the vomer appears as a rod of o s s i f i c a t i o n along the mid-line of the bone to be. At t h i s stage i t i s of no great degree of development but i n d i c a t e s the pos-i t i o n , and gives some idea of the snape and s i z e of the v e n t r a l part of the bone. By 28 mm. of length t h i s has developed i n t o a f l a t t e n e d long narrow t r i a n g u l a r shaped bone being quite f l a t at i t s a n t e r i o r extremity. No i n d i c a t i o n i s yet present as to the development of the a n t e r i o r mass of the adult bone. At t h i s time the a n t e r i o r p o r t i o n i s very close to the t i p of the para-sphenoid, almost as a suture, a c o n d i t i o n which a c t u a l l y never occurs. Some teeth appear along t h e - a n t e r i o r mid-line of the v e n t r a l p a r t of the bone at 28 mm. The mass about the a n t e r i o r t i p remains incomplete u n t i l some time a f t e r the 39 mm.stage, when the l a t e r a l arms are mere t i p s , as i s the d o r s a l horn, while the v e n t r a l body i s q u i t e wide comparable to i t s mature shape. The ethmoid bone al s o appears at 26 mm. of l e n g t h as a mass of o s s i f i c a t i o n i n the region of the d o r s a l c r e s t of the body. This p a r t of the bone continues to develop f a i r l y consis-t e n t l y through to the" 28 mm. stage when the l a t e r a l arms 'become apparent as w e l l as the postero-dorsal wings which are l i g h t l y o s s i f i e d . A t 30 mm. the wings are w e l l developed but separate from themselves and from the body region whichais l i g h t l y formed. At 39 mm. the l a t e r a l and p o s t e r i o r d o r s a l arms are -30-quite w e l l formed as i s the do r s a l am&s-tbut the body mass i s rather l i g h t l y o s s i f i e d . I n the mature forms studied the ventral part of the body was apparently l e s s densely o s s i f i e d than the other p o r t i o n s . The p r e f r o n t a l s show development i n the region of the p o s t e r i o r d o r s a l wings at 26 mm., a s i t u a t i o n which p e r s i s t s even u n t i l the 39 mm. specimens when the bone i s l a c k i n g i n i t s body parts and c o n s i s t s mainly of the p o s t e r i o r d o r s a l wings j u s t about the o r b i t . The 39 mm. specimen shows a curved wing-l i k e s t r u c t u r e forming the a n t e r i o r and antero-dorsal borders of the o r b i t . None of the heavier body part i s present as yet. At 26 mm. the p t e r o t i c bone shows a small o s s i f i c a t i o n mass i n the region of the l a t e r a l c r e s t . Prom t h i s point o s s i -f i c a t i o n spreads inward about trie bone s t r u c t u r e so that.at 30 mm. the l a t e r a l r egion i s quite w e l l o u t l i n e d as i s the post-temporal a r t i c u l a t i o n . In the 39 mm. specimen a l l of the bone i s apparent except the p o s t e r i o r p r o j e c t i o n of the l a t e r a l c r e s t . I t i s , however, quite separate from i t s neighbours. Of the o c c i p i t a l , bones the b a s i - o c c i p i t a l shows o s s i f i -c a t i o n about the surface of a small curved cone with i t s t i p t u r n e d w e n t r a l l y . Prom t h i s c o n d i t i o n , as at the 26 mm. stage, the bone develops i n i n t e n s i t y and mass,until the 39 mm. spec-imen shows a s o l i d l y o s s i f i e d mass more l i k e the mature form, having l o s t the cone appearance which p e r s i s t s u n t i l 33 mm. At 28 mm. the wing developments appear along the sides of the cone and continue t i l l 39 mm. when they are fused w i t h the cone mass. -31-The e x o c c i p i t a l s show very s l i g h t o s s i f i c a t i o n at 26 mm. but at 27 mm. appear with o s s i f i c a t i o n along the medial and more p o s t e r i o r medial p a r t s . Growth continues so that at 33 mm. the o u t l i n e of the bone i s quite d e f i n i t e and at 39 mm„ seems to be complete. As i n other bones of t h i s region at 39 mm. the bone i s quite widely separated from i t s neighbors. The supensory system of the hyoid apparatus appears at the 27 mm. stage. The p r i n c i p a l bone of t h i s Sj stem, the rijo-mandibular, shows traces i n the main body part at t h i s stage, i . e . the d o r s a l h a l f of the bone i n the region of the connec-t i o n to the p t e r o t i c and to the operculum, u i s t a l l y , or vent-r a l l y towards the pterygoid bones, there seems to be a massive c a r t i l a g i n o u s development,rather squared o f f than tapered as i n the adult form. This shape continues past the 39 mm. stage as studied. By 39 mm. the a r t i c u l a t i o n w i t h the p r o o t i c i s w e l l formed and the symplectic bone seems to be i n proper p o s i t i o n , a l s o towards the operculum the hyomandibular has quite good development, but i n the region of tne metapterygoid the exact j u x t a p o s i t i o n of the bones i s i n d e f i n i t e , w i t h the hyomandibu-l a r of no p a r t i c u l a r o u t l i n e i n d i e a t i n g the mature form, and the metapterygoid i n d e f i n i t e l y formed along the edges. The symplectic bone appears as a small d i a p h y s i s - l i k e centre at the 27 mm.. stage. There remains only growth i n length and density to a t t a i n the mature form. This develops through the 39 mm. stage where the t i p s are as yet i n d e f i n i t e l y formed. The e p i h y a l f i r s t appears at 27 mm. as a small c e n t r a l o s s i f i c a t i o n which develops p r i n c i p a l l y along the dorsal- edge -32-of trie bone. At 28 mm. another centre appears more v e n t r a l l y , but united to the f i r s t centre at the p o s t e r i o r angle,so that the whole i s now a somewhat V-shaped s t r u c t u r e , open a n t e r i o r l y . This .continues developing i n s i z e and density u n t i l , i n the 30 am stages, there i s a good degree of development along the l i n e of one mass s l i g h t l y vee'd a n t e r i o r l y . At 39 mm. there i s a good degree of development along the d o r s a l and v e n t r a l edges and p o s t e r i o r l y , but a l i g h t e r area remains toward tne middle. Pos-t e r i o r l y , i n the region of the suspensory point, considerable development i s l a c k i n g . The urohyal begins as a rod of o s s i f i c a t i o n along i t s v e n t r a l edge at 27 mm. This continues to develop i n density for some time, the blade part not appearing u n t i l the 30 mm. stage. At 33 mm. the bone i s f a i r l y complete and at 39 mm. good de-velopment i s present. The a n t e r i o r t i p i s quite f a r from the b a s i - h y a l s . The o r b i t a l bones also f i r s t appear at 27 mm. with two s l i m centres i n the p r e o r b i t a l region, four i n trie s u b o r b i t a l , two of which l a t e r fuse a f t e r 39 mm. to form the f i r s t subor-b i t a l . The s u p r a o r b i t a l also appears at t h i s stage as a long s p l i n t e r of bone. A l l of these bones c l o s e l y r i n g i n g the o r b i t are formed along the edge c l o s e s t to the o r b i t and develop from t h i s . The others, the p r e o r b i t a l s , form i n i h e i r c e n t r a l parts and develop around from t h i s centre. .Development of none i s very complete at 39 mm. In the cranium the sphenotic bone has a small o s s i f i c a -t i o n at i t s a n t e r i o r t i p at 27 mm. stages. Growth i s slow,with -33-l i t t l e new'development u n t i l 33 mm. stages, when the o s s i f i c a -t i o n has passed i n t o some of the' body of the bone along the an-t e r i o r and l a t e r a l p a r t s . At 39 mm. most of the structure i s present i n i t s outer surfaces, but i t i s one of the l e s s com-p l e t e l y formed members of the cranium bones at t h i s stage. The p o s t e r i o r p l a t e of the s u p r a o c c i p i t a l appears b.> the 27 mm. stage. At 30 mm. the medial part of the dorsal sec-t i o n of the bone shows, and the p o s t e r i o r part has extended. In tne 33 mm. specimens most of tne dor s a l part has formed, and by the time of 39 mm. length the bone i s quite complete, with the dors a l ridges w e l l formed ana only the v e n t r a l edge of the pos-t e r i o r p l a t e l a c k i n g very much from complete formation. The l a s t of the suspensory bones of the hyoid system appears at 30 mm. when the i n t e r h y a l appears as a short tubular o s s i f i c a t i o n of l i g h t development. The l a t e r formation of t h i s bone i s s l i g n t l y i n leng t h and diameter, but mostly f o r depth, and at 39 mm. i t i s quite w e l l formed, althougn not completely o s s i f i e d through. I t seems to nave been preformed i n c a r t i l a g e and o s s i f i e s around the perichondrium of the s t r u c t u r e . At 39 mm. i t i s s t i l l a hollow s t r u c t u r e . In t h i s region, at 30 mm., the branchiostegals f i r s t appear w i t h three p a i r s borne on the ceratohyal and three p a i r s on the e p i i i y a l . At 33. mm. the most a n t e r i o r p a i r i s i n d e f i n i t e , so as to be almost l a c k i n g , but at 39 mm. the eight p a i r s are a l l w e l l formed. The p o s t e r i o r three p a i r s are t h i n and membra-nous, while the a n t e r i o r ones are quite deeply o s s i f i e d and f a i r l y stout. -34-A small i r r e g u l a r o s s i f i c a t i o n appears at 30 mm. i n the more dorsal and medial parts of the metapterygoid. The develop-ment i s quite l i g h t , and may be missed quite e a s i l y , but i s present as the f i r s t stages of o s s i f i c a t i o n i n the bone. At 33mai. the formation continues to a small extent, but by 39 mm. most of the bone i s apparent, although i t i s not yet complete i n i t s d i s t a l parts so that contact i s not apparent to any of the sur-rounding bones. The l a s t bone of the pterygoid system to be considered i s the p a l a t i n e , which shows a rather c y l i n d r i c a l shape at 30mm., continuing qui te t h i n l y o s s i f i e d at 33 mm. In the 39 mm. stage the a n t e r i o r shape forms, but the bone i s t h i n l y formed i n most of i t s o u t l i n e . A r t i c u l a t i o n s at i t s t i p , as with the maxillary, and contact with the ethmoid.arms are not yet i n d i c a t e d . In the sphenoid region p o s t e r i o r and dorsal to the eye, development f i r s t shows i n the 30 mm. specimens,at which time the alisphenoids show curved o s s i f i c a t i o n s i n t h e i r l a t e r a l edges, and the orbitospnenoid shows two masses close to the f r e n t a l s i n the l a t e r a l edges of the bone. This c o n d i t i o n i n -d i c a t e s the p a i r e d source of the bone, but by 33 mm. there i s but one mass of o s s i f i c a t i o n , passing from the o r i g i n a l parts to the centre and there f u s i n g . The f u s i o n i s so much sooner than any other bones esen meet to contact that apparently t h i s i s a s i n g l e bone i n t h i s species, forming from two centres. At 39 mm. the o r b i t o sphenoid development i s quite l i k e the ma* ture bone wi t h the exception of the a n t e r i o r medial s e c t i o n to the p r e f r o n t a l s . The f u s i o n i n the midline below the f o r e b r a i n -35-i s quite d e f i n i t e and s o l i d . The alispnenoids develop by growth, from the outer edges inward so tnat i n the 39 mm. specimen the c o n d i t i o n i s very s i m i l a r to the a d u l t , except f o r wide fissures surrounding i t . Along the v e n t r a l side of the cranium a s p l i n t - l i k e o s s i f i c a t i o n mass i n d i c a t e s the o p i s t h o t i c at 30 mm. This i s p r i n c i p a l l y at the p o s t e r i o r t i p of the bone i n the region of the p o s t e r i o r a r t i c u l a t i o n to the post-temporal bone. Develop-ment i s required towards the a n t e r i o r part of the bone and i n mass. This continues to 39 mm., wnen a good part of the bone i s evident, l y i n g quite separated from tne o s s i f i e d parts of the p r o o t i c , e x o c c i p i t a l , and p t e r o t i c , which fuse l a t e r . The nasal shows as an i n d e f i n i t e b i t of o s s i f i c a t i o n at 30 mm., developing to a curved piece by 33 mm,,and i n the specimen of 39 mm. i t i s a w e l l formed stiape of o s s i f i c a t i o n showing much of the mature s i t u a t ion. Of the remaining bones to be found, the p a r i e t a l and basisphenoid show at 33 mm. as t a i n i n d e f i n i t e developments. The p a r i e t a l i s w i t h d i f f i c u l t y made out apart from the f r e n -t a l s u n t i l 39 mm., when i t s o u t l i n e i s s u f f i c i e n t l y o s s i f i e d to be l o c a t e d i n proper r e l a t i o n to the other bones of the re-gion. Most of the shape of the bones i s apparent at t h i s stage. The basisphenoid i s present as^J-lghtly o s s i f i e d bar at 33 mm., development proceeding i n the ends of this, so that at 39 aim. a more d e f i n i t e H-shape i s seen witn i t s parts w e l l o u t l i n e d i n r e l a t i o n to the other bones of the region. Medially the ven-t r a l p r o j e c t i o n i s not yet present. -36-The l a s t of the bones to appear i n the specimens under consideration was the e p i o t i c . At 39 mm. t h i s bone snows a cap of o s s i f i c a t i o n about the surface of the curved apex, where the t i p forms f o r the post-temporal aonnection. The mass of the bone i s i n a c a r t i l a g i n o u s s t r u c t u r e at t h i s stage. Small teeth are beginning to appear i n the region of '. the glossohyal at 39 mm. J N O development i s present i n the bone mass. DISCUSSION In the l a s t stage studied there appeared to be quite good development i n a l l of the bones as considered i n the ob-ser v a t i o n s e c t i o n . Any d i f f e r e n c e i n development seems to be i n the degree to -which the membranous bones are developed as com-pared to the bones i n the region of tne chondrocranium,see P l a t e VII, Figs.XIV,XVI. P r a c t i c a l l y a l l of these msmbranous bones are completely formed to the greatest l i m i t s of t h e i r growth, whereas the endochondral bones are developed so as to i n d i c a t e shape and p o s i t i o n , but are not deeply o s s i f i e d or to, i n some cases, anywhere near approximating t h e i r f u l l e s t extent of growth. There may be some s i g n i f i c a n c e i n the f a c t that, i n general, the membranous bones are formed before the endochon-d r a l bones. In the 22 mm. specimens the best development i s i n the e x t e r i o r membranous bones, as of the opercular system and membranous parts of the jaws. S t i l l l a t e r , as at 26 mm., these external systems remain b e t t e r developed r e l a t i v e l y to the c r a n i a l p a r t s . I t seems , from the order of appearance of the bones, that t h i s p r i o r i t y of the membranous development could be r e l a t e d to the conditions of l i f e of the growing f i s h . In the tables the bones are l i s t e d w ith regard to the general order of appearance, Table I l i s t i n g them i n the order of t h e i r f i r s t showing by the a l i z a r i n s t a i n method, and as tney are considered i n the observations s e c t i o n of the paper. Table I I groups the bones i n t o systems, and the time of ap-pearance of the members of the systems. The systems are arran--38-ged on a basis of the appearance of the f i r s t noted member. From t h i s i t can be seen that among the e a r l i e s t systems are those i n v o l v i n g membranous bones, while those appearing l a t e r , or even the l a t e r of the members of any system are bones more nearly formed from c a r t i l a g e . According to Gwynn (1) the vertebrae are 'represented by. r i n g s of bone developed i n the exte r n a l e l a s t i c sheath of the notochord at 28 mm.' This stage corresponds to the 26 mm. specimens of t h i s paper. The leng t h d i f f e r e n c e i s a r e s u l t of the technique of measurement used. The 28 mm, i s from the t i p of the snout to the t i p of the t a i l , whereas the 26 mm. i s taken from the t i p of the snout to the base of the t a i l f i n . Both are taken from specimens i n the same c o l l e c t i o n taken on the same day, May 16, 1932, at Nanoose Bay. In the head at t h i s stage the b a s i o c c i p i t a l i s represented as a hollow cone of o s s i f i c a -t i o n , which i s comparable to the s i t u a t i o n recorded f o r the vertebrae. The same author reports that the vertebrae are i n a f a i r l y complete stage of development, showing c e n t r a l c o n s t r i c -tions and development of the a r c u a l i a at 39.4 mm. The same con-d i t i o n was observed i n the 39 mm. specimen observed here. These observations on the c o n d i t i o n of the vertebrae are i n accord w i t h the other bones preformed i n c a r t i l a g e , and appearing on the whole l a t e r than those not so formed. This preparatory viewing of the s i t u a t i o n i n the o s s i f i -c a t i o n of the bones of the head seems to i n d i c a t e that the ear-1. Gwynn, A.M.,I.e. p.4. e se -39-l i e s t bones to form are among the more u s e f u l members of the head skeleton, F i r s t - from the point of necessity jaw bones ap;f-pear, then such bones as the opercular system, also required from the p h y s i o l o g i c a l nature of t h e i r f u n c t i o n . Supporting member^oiOf;;i:t,h;&se systems f o l l o w c l o s e l y , while bones of a mor i n d i r e c t n e c e s s i t y , as i n the cranium, appear l a s t . In the ca of these l a s t , t h e i r f u n c t i o n of support and p r o t e c t i o n f o r the brain i s f u l f i l l e d before t h e i r appearance by the chondrocra-nium s t r u c t u r e . Also bearing t h i s out i s the development of the f r o n t a l bone, one of the e a r l i e r bones to form, yet belonging to the c a r t i l a g e bones of^the s k u l l , i n part. The p r o t e c t i v e f u n c t i o n of t h i s bone wi t h regard to the br a i n removes i t from c l a s s i f i c a t i o n w i t h other bones of the cranium as to i t s time of appearance. -RO-TABLE I Bones arranged i n Time of appearance: order of appearance. 14 mm. 22 mm. 26 mm, 27 mm. 50 mm. 35ma, Dentary x M a x i l l a r y x Premaxillary x Admaxillary x A r t i c u l a r x Quadrate x Opercle x Preopercle x Interopercle x Parasphenoid x P r o o t i c x F r o n t a l x Mesopterygoid x Subopercle x Pterygoid x Ceratohyal x B a s i h y a l x Vomer x . Ethmoid x P r e f r o n t a l x P t e r o t i c x B a s i o c c i p i t a l x E x o c c i p i t a l x Hyomandibular x Symplectic x E p i h y a l ' x Urohyal P r e o r b i t a l S u p r a o r b i t a l x Su b o r b i t a l x Sphenotic x S u p r a o c c i p i t a l x I n t e r h y a l Branchiostegals x Metapterygoid x P a l a t i n e x Alisphenoid x Orbitosphenoid x O p i s t h o t i c Nasal P a r i e t a l x Basisphenoid . - * E p i o t i c n (l #Glossohyal " x x x X X X Table l i s t i n g tne bones appearing at stages studied i n tne text. #Thi s bone, i s only s l i g n t l y i n d i c a t e d at 39 mm. -41-TABLE I I Bones arranged i n Order of xype of bone: systematic groups Appearance Membrane Ca r t i l a g e Dentary X -——— —. i. ,—.—m— ^ X A r t i c u l a r X X / / a x i l l a r y X X P r e m a x i l l a r y X X Admaxillary X X Opercle X Preopercle . X X Interopercle X X Subopercle X X yuadrate X X Pterygoid X X Mesopterygoid X X metapterygoid X X P a l a t i n e X X x Byomandibular X x symplectic X X I n t e r h y a l X X E p i h y a l X X X Geratohyal X X B a s i h y a l X X Qlossohyal X X uroh.yal X X Branchiostegals X X suborbi t a l X X P r e o r b i t a l X X bupraorbi t a l X X .Nasal X X F r o n t a l X X Parasphenoid X X P r o o t i c X X •Vomer X X Ethmoi d X X P r e f r o n t a l X X X P t e r o t i c X x B a s i o c c i p i t a l X x E x o c c i p i t a l X X Sphenotic X X S u p r a o c c i p i t a l X X A l i sphenoid X X Orbitosphenoid X X O p i s t h o t i c X X P a r i e t a l X X E p i o t i c X X Table to i n d i c a t e the trend of the order of appearance of the bones i n systems. -42-NOMENCLATURS In the ethmoid region there develops a problem as to the correct designation of c e r t a i n of the bones, wi t h a view to the homology of the members. Considering the chondrocranial o r i g i n there i s expected a mesethmoid, and two ectethmoid bones, but i n the work on synonymy by Starks ( l ) there are the ethmoid and no others. The p r e f r o n t a l s could be the hoaolgy,in part,of the ectethmoids,except that there are the membranous wings which may a l s o be the homolgy of the p r e f r o n t a l s of R e p t i l i a . I f the homology i s to be c a r r i e d completely' the names used herein may be changed to ectethmoids, and a mesethmoid, but since i n some cases homolgy can be s t r a i n e d no cnange was made from the work on synonymy r e f e r r e d to. Further work along t h i s l i n e seems to be i n d i c a t e d . Upon f u r t h e r study of the sphenoid s i t u a t i o n there has occured the p o s s i b i l i t y of the orbitosphenoid here used being made up of the two orbitosphenoids and the s i n g l e presphenoids bones f u s i n g to produce the s t r u c t u r e seen, witn the l a t e r a l p l a t e s as orbitosphenoids and the medial blade as the pre-sphenoid. This, a l s o , c a r r i e s the p o s s i b i l i t y of work along the l i n e s of synonymy and homolgy i n the lower vertebrata* 1. Starks, E.G.,I.e.p. i i . SUMMARY The general anatomy of the head bones of the a e r r i n g has been presented, and i s i l l u s t r a t e d i n P l a t e s I-IV. The time and order of appearance of the member bones has been considered over the period of time during which a l l of the bones appear, at l e a s t i n i n i t i a l stages. Some a t t e n t i o n has been paid to the i n t e r r e l a t i o n of the times of appearance of the bones as to groups and s i n g l y . P l a t e s V-VIII give some idea of the conditions of the bones during c e r t a i n stages of t h e i r growth. A l l of the photographs are from specimens i n g l y c e r i n e a f t e r a l i z a r i n s t a i n i n g , as explained i n the tecanique s e c t i o n . In the process of the work c e r t a i n d i f f i c u l t i e s to do w i t h the a s s i g n i n g of names to the bones,and with regard to t h e i r homologies have been shown to e x i s t . As a c o n c l u s i o n , i t i s hoped that these researches w i l l be of value i n the f u r t h e r pursuing of any work passing on from these p o i n t s . In d i r e c t l i n e i s the chondrocranial development and other d e t a i l s of osteogenesis, while l e s s d i r e c t l y apparent, and probably more important i s the problem of nomenclature throughout the Glass. PLATS v .Dentary -Maxillar Dentary A r t i c u l a r M a x i l l a r y B a s i h y a l Ceratohyal Urohyal — Parasphenoid •Quadrate P r o o t i c Opercle Pig- VII Ventral view of 22 mm. stage, -Dentary -Premaxillary -Maxillary -Ethmoid Preopercle • -Parasphenoid -Preopercle P i g . v I I I V e n t r a l ; P i g . Ix Dorsal views of 28 mm. l a r v a l stage. Prontal-P r o o t i c-C l a v i cle-E r o n t a l P r e f r o n t a l Ethmoid M a x i l l a r y Parasphenoid Dentary Pterygoid A r t i c u l a r Ceratohyal uadrate g i g . A L a t e r a l view of 28 mm. stage, PLATS VI •Dentary P r e m a x i l l a r y M a x i l l a r y Vomer Ethmoid l a s a l P r e o r b i t a l P r e f r o n t a l Pterygoid Hyomandi bular-P t e r o t i c Opercle Orbitosphenoid Fr o n t a l Alispaenoid Parasphenoid P r o o t i c P t e r o t i c — S u p r a o c c i p i t a l — E x o c c i p i t a l — B a s i o c c i p i t a l Frontal-P r o o t i c Supraoccipi t a l . E p i o t i c F i g s . XT, XIT, XIIT Doxsal views at d i f f e r e n t o p t i c a l planes of the 39 mm. l a r v a l stage. -45-PLATE VII Ethmoid P r e f r o n t a l Dentary Pterygoid M a x i l l a r y Preopercle Ceratohyal B a s i h y a l A r t i cular (JlossoAjal ^teetnj P i g . XIV To chcv; dsgrea of development of membrane bones. Proo t i c Hy omandibular Opercle Preopercle P i g . Xv To show bran c h i a l apparatus and suspensorium. Suborbitals Metapterygoid jites op tery go i d P terygoid Symplectic Quadrate A r t i c u l a r ngula'r •Branchiostegals P a r i e t a l E r o n t a l A l i spnenoid Orbitosphenoid Sphenotic Suborbi t a l s Hyomandibular Parasphenoid Preopercle F i g . Xvl To show cranium ana degree of development of membrane bones i n p o s t e r i o r region. F i g s . XIV, XV, XVI L a t e r a l views of 39 mm. l a r v a l stages. "46-E p i o t i c P t e r o t i c E x o c c i p i t a l P r o o t i c vertebrae Opercle P L A T E V I I I Bpi o t i c . Parasphenoid P r o o t i c Hyomandibular P t e r o t i c Opercle O t o l i th B a s i o c c i p i t a l E x o c c i p i t a l P i g . A V I I Ventral view of cranium of 39 mm. l a r v a l stage, showing attachment of suspensorium to p t e x o t i c and degree of c r a n i a l development. -47--49-BIBLIOGRAPHY Part One, L i t e r a t u r e Cited: Cumley, R.W., Crow,J.P., and G r i f f i n , A.a., 'Clearing specimens f o r the Demonstration of Bone'. S t a i n Technology. 1 4 ( l ) , Jan. 1939 pp. 7-12. Gwynn, Agnes M., 'A Study of the Development of the Vertebral Column i n the P a c i f i c Herring'. Thesis, U.B.C., 1938. Jordan, David S t a r r , 'A Guide to the Study of Pishes'. Henry Holt and Company, 1905. Starks, Edwin Chapin, 'The Synonymy of the P i s h Skeleton'. Washington Academy of Sciences, 1901. HThit taker, ¥.R. , 'The Anatomy of the North American P i l c h a r d ' . Thesis, U. B. C., 1932. Part Two, L i t e r a t u r e Consulted: Goodrich, Edwin S.,'Studies on the Structure and Development of Vertebrates'. Macmillan and Co., 1930. Hyman, L i b b i e Henrietta,'A Laboratory Manual f o r Comparative Vertebrate Anatomy'. U n i v e r s i t y of Chicago Press, 1936. Kingsley,J.S.,'The Vertebrate Skeleton'. John Murray, 1925. 'Outlines of Comparative Anatomy of vertebrates'. P. B l a c k i s t o n ' s Son and Go. 1926. Tomkinson,William, 'On the con d i t i o n of the Gat Skeleton at B i r t h ' . (Por Methods) Thesis, U.B.C., 1936. 

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