"1'°-'1 5 A, S'WDY GF THE GSTEOLOGY OF THE AMERICA?! SMELT, QSMERUS MORDAX { MiTCHlL‘.) Thesis for tho Dogm :4 Ph. D. MICHIGAN STATE UNEVERSiTY Jaga‘t Pa! Singh 1959 This is to certify that the thesis entitled The Osteology of the American Smelt (Osmer'us mordax) presented by Jagat Pal Singh has been accepted towards fulfillment of the requirements for Ph.D. degree in Fisherx Biology flaw Major professor Date March 5, 1959 LIBRARY Michigan State University A S‘I‘UZX C Submitted to Michigan 5: Soience 1; De; Approved\{ A STUDY OF THE OSTEOLOGY OF THE ARERICAN SKELT, OSRERUS MORDAX (MITUHILL) By JAGAT PAL SINGH AN ABSTRACT Submitted to the School for Advanced Graduate Studies of Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Fisheries and Wildlife 1959 Approved__@ 0 ' M .- 315: under the ufilh and 5' The s. afthe short The 0 :ref‘rontals, The 0 553188 of Do: The c par: 38.16 , pr‘ Paired exocc: .i t AN ABSTRACT The American smelt, Osmerus'mordag (Hitchill) is classi- fied under the family, Osmeridae by recent ichthyologists, Berg (1940); and Hubbs and Lagler (1947). The skeleton of the smelt is typical of teleostean fishes of the suborder, Salmonoidea. The olfactory region contains the paired proethmoids, prefrontals, vomers, nasals and the unpaired ethmoid. The orbital region contains the paired circumorbital series of bones, frontals and sphenotics. The otic region contains the paired pterotics, epiotics, parietals, post-temporals and the unpaired supraoccipital, the paired exoccipitals, prootics and supracleithrums. The basicranial region contains the unpaired basioccipi- tal and parasphenoid. The oromandibular region contains the paired palatines, quadrates, articulars, metapterygoids, entOpterygoids, ptery— goids, premaxillaries, maxillaries, supramaxillaries, angulars and dentaries. The hyoid region contains the paired hyomandibulars, symplectics, interhyals, epihyals, ceratohyals, hypohyals, oper- culars, preOperculars, subOperculars, interoperculars, branchi- ostegals and the unpaired basihyal and urohyal. The branchial region contains the paired pharyngo— brzchials, epi cf the unpairc The eke ifferences su: 525111 the 36: retaining the: The ve: peivic fine, a the ”Meal te ii branchials, epibranchials, ceratobranchials, hypobranchials and the unpaired basibranchial. The skeletons of the smelt and the salmon show differences sufficient for recent ichthyologists to classify them in the separate families,Osmeridae and Salmonidae, but retaining them in the same suborder, Salmonoidea. The vertebral cblumn, dorsal fin, pectoral fins, pelvic fins, anal fin and caudal fin are very similar to the typical teleostean fishes. d ' hte 1g copygy Singh t Pal Jaga 1961 [flfi P.“ AS I V "‘ . Lil-b V‘ in: tted to ‘ nonigan St: Science in A STUDY OF THE OSTEOLOGX OF THE AMERICAN SMELT, ggmsaus MORDAX (MITCHILL) By JAGAT PAL SINGH A THESIS Submitted to the School for Advanced Graduate Studies or Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Fisheries and Wildlife 1959 APproved I am gr 1532mm of E titan in my I" For e1 Lsagain ince‘: I wi 51 for many sue; "(T-1‘] .r'v " C/Zth/{ct ACKNOWLEDGMENTS I am greatly indebted to Dr. Peter I. Tack, Head of Department of Fisheries and Wildlife for his guidance and super— vision in my research work. For all photographs of the various bones, the author is again indebted to the professor P. I. Tack. I wish to express my gratitude to Dr. Eugene W. Roelofs for many suggestions and advice. iii onJA'YV‘W". "j . ,. “IV-r1. J - V8". 0 o .i— .V I._-‘ ...v— A. ‘ I" . :‘;:J‘fi “Ala-l DA dU‘ ,p , u 7‘ - VT‘. ..'- Jug-‘Jub khan-J Alo— n..-..—n.-Qp. r -‘ — U;;.-‘|.‘JO&J" V: k ‘A. fil“-~l‘, l . J _ .' —‘ a Vuuun..‘DV“ V: i 95- ,_ . L‘:1—"J~Tfl\v -_. “"L-«4 ‘L 1 " V.- V- E"!- 'Q" .",-:.y.",‘1'r~.». ~v... 1 h— ¢¢‘LU“ U: u. 7"“-I-"W’ .. ‘. 4'.~. ._ is)...‘u L , > - ‘ V65 b.‘ 3““. . ‘ ‘ vi 4 \; uq’TW‘ U~JJ~ Dfi’lfi,‘Y 5‘ ‘~“ ‘ l 1 ‘LVAt V. ‘Gn- .\ ’ M, ‘ n“. -‘N‘Nep . L r ‘ . V.‘ b; T‘?~~~-\ d ‘ d . -.‘ A‘ ‘54.}.“r T ‘ v (‘- ‘s _: V— L M. .‘ :1. “A" ‘N..- "~U:' n. . ‘ ~.'~*L\J D - 17-..- \—.. ‘ $51.." : .1. \ "-, -H U“'..n“‘( ‘ TABLE OF CONTENTS PAGE INTRODUCTION. . 1 GEHERA AND SPECIES. . . . . . . . . . 3 MATERIALS AND METHODS . 12 DESCRIPTIOE OF OSTEOCRAAIUM OF THE ShELT (OSKERUS MORDAX) 14 (a). Olfactory region . . . . 21 (b). Orbital region 22 (c). Otic region. 26 (d). Basicranial region . . . . . . 28 (e). Oromandibular region . 29 (f). Hyoid region . . . . 32 (g). Branchial region 41 COMPARISON OF SLELT'S SKULL WITH SKULL OF SALAON. 43 DESCRIPTION OF VERTEBRAL OOLUAN OF SHELT (OSAERUS EORDAX) 59 DESCRIPTION OF LORSAL PIN OF SMELT (OSLERUS MORDAX) . 67 DESCRIPTION OF PEOTORAL GIRDLE AND FIN OF SMELT (OSHERUS MORDAX) . . . . . . . . . . . . . . . . . 71 DESCRIPTION OF PELVIC FIN OF SKELT (OSMERUS AORDAX) . 76 DESCRIPTION OF ANAL FIN OF SAELT (OSAEBUS MORDAX) 82 DESCRIPTION OF CAUDAL FIN OF SAELT (QSAERUS MORDAX) . . . 86 PHILOGENETIC RELATIONSHIP OF THE SAELT IN TELEOSTEAN FISHES. . . . . . . . . . . . . . . . . . . . . . 92 swam 97 . lOO LITERATURECCITSULTE................. iv In \f‘ " n p .. “L:- uUA'a SA-...-.C A TABLE TABLE PA GE I. THE COMPARISON OF VARIOUS BONES OF SKULL OF THE SALI'EON ADID ill-{E SI‘ELT. o o o o o o o o 57 True America: 3:31]. Of LLB ‘ . 0 $- . 31.11 OJ. tn: ,..- 1.. a Segue; se ncr‘afl FIGURE PAGE 1. The American Smelt, Osmerus mordax (Hitchill). . . . 8 . Skull of the smelt (Osmerus mordax); lateral view. . 16 2 3. Skull of the smelt (OsmeruS‘mordax); lateral view. . 18 h. Sagittal section of the skull of the smelt (Osmerus mo maX) . . . O O C . O O C C . C 0 . 0 C . O C O 20 5. Skull of the smelt (Osmerus mordax), dorsal view . . 2h 6. Skull of the smelt (Osmerus mordax), dorsal view . . 2S 7. Hyobranchial system of the smelt (Osmerus mordax), dorsal View 0 o o c o c o c o c o o o c I o o o 0 3L!- 8. Hyoid arch, left half of the smelt (Osmerus mordax), mesial View . . . . . . . . . . . . . . . . . . . 36 9. The preoperculars from skull of the smelt (Osmerus mordax), lateral view . . . . . . . . . . . . .. 39 10. Skull of Salmo sp., lateral View . . . . . . . . . . MS 11. Skull of Salmo Sp., dorsal view. . . . . . . . . . . h? 12. Skull of the smelt (OsmeruS‘mordax), lateral view; . A9 13. Skull of the smelt (Osmerus mordax), dorsal view . . 51 1A. Description of vertebrae of the smelt (Osmerus mordax)61 A. First vertebra (Atlas), posterior view B & C. A typical vertebra (3-hl), posterior view D. Caudal vertebra, posterior View 15. Vertebral column with the caudal fin of the smelt (Osmerus morda‘t) . . . . . . . O . . 0 . . . . C . 63 16. Dorsal fin of the smelt (Osmerus mordax) . . . . . . 69 17. Left coracoid, scapula, cleithrum and pectoral fin of the smelt (Osmerus mordax), mesial View . . . . . 73 vi qt- .5. m . .O‘ a 18. 19. 20. 21. 22. LIST OF FIGURES (Contd.) Left pelvic fin of the smelt (Osmerus mordax), lateral Vietq. O O O O O O I O O D O O O O C O O O O O O O O Pelvic fine of the smelt (Osmerus mordax), lateral View. 0 O C . . C O 0 Anal fin of the smelt (Osmerus mordax) . . . . . . . . Caudal end and caudal fin rays of the smelt (Osmerus mordax). Diagrammatic. . . . . . . . . . . . . . . Caudal end and caudal fin rays of the smelt (Osmerus morda-lvb ) C O O C O O O O O O O O 0 O C O O O O C O 0 vii INTRODUCTION The . isclassifie at Berg (IE frilies SaI Gibbs and I 21313 a 3 three gene]: 3'6 placed T .118 gener a INTRODUCTION The common American smelt, Osmerus mordax (Mitchill) is classified under the family Osmeridae by Jordan (I929) and Berg (I9h0). The family Osmeridae is closely related to families Salmonidae, Coregonidae, Thymallidae and Argentinidae (thbs and Lagler, I9h7), (Jordan, I905), and (Berg, I9h0). This is a small family with 7 genera and I3 species. Only three genera are listed by Berg (19,10). These three genera are placed in the two subfamilies, Osmerini and Hypomesini. The genera Osmerus and Mallotus are placed under the sub- family Osmerini, while the genus Hypomefiis is placed under the subfamily Hypomesini. The osteology of genus Mallotus is completely unknown. Berg gave the diagnostic subfamily characters of Osmerini as follows: (I) Olfactorius passing through the orbit. (II) Mesethmoid paired in young. (III) Vomers sometimes paired in young. The diagnostic charact- ers of Hypomesini are (I) Olfactorius nerves not passing through the orbit. (II) Teeth feeble. (III) No canine on vomer. (IV) Mesethmoid and vomer unpaired. No attempt has hitherto been made to describe the osteodbgy of the smelt, Osmerus mordax, though Starks (19%) has described the ethmoid region of the smelt, Osmerus dentex. Excellent figures of Salmo sp., closely related to the smelt are described by Gregory (I933). GENERA AND SPECIES ,4..I~...&\ We" ens; ) . z. : ~ “"_‘\ R ' Law-:5 “AU. er.‘ I...JSe ,- ‘0’. enemal 0;; l .r. till 3:: s l.) EIWRFQ ‘L"-\- 8r{ ‘ e. zap-x ‘ “a “"§d,lg r ‘ C rs.” ~A Ehh “I-“al ..I;a.- Vu‘ ‘ u. ‘ ' J. GENERA AND SPECIES There are 7 genera of smelt containing 13 species. For convenience, each genus is briefly characterized below. The species with their characters are listed under the corresponding genus. I. Genus Mallotus Cuvier External characters: (I) Scales very small, arranged in males in villous bands. (II) Pectoral fins broad, of 15 to 20 rays. (III) Teeth feeble. (IV) Pyloric caeca, six. (V) Branchios- tegals 8 to 10. (VI) Dorsals inserted over ventrals. (VII) Gill rakers long and slender. Mallotus villosus (Muller). Characters: (a) D.12; A.l8, scales about 150. (b) Head long and pointed. (0) Base of anal in males compressed and prominent, its anterior rays simple and stiff.‘ (d) Pectorals reaching more than halfway to ventrals and the latter reaching more than halfway to anal. II. Genus Thaleichthys Girard External characters: (I) Teeth feeble, those on tongue very weak. (II) Scales small, adherent and similar in both sexes. (III) All the teeth are very feeble, slender, and deciduous, although occasionally present on all the bones of the mouth; no permanent teeth on the tongue. (IV) Coloration dusky. Thaleichthy§_pacificus_(Richardson): Characters: (a) It D.ll; A.21; P.ll; scales 75. (b) Pyloriccaeca 11. (0) Ver— tebrae 70. (d) Mouth large, the maxillary rather narrow and long, reaching beyond the middle of the rather small eye. (e) Lower Jaw projecting. (f) Opercle with strong concentric striae. (g) Gill rakers are numerous, rather long and slender. (h) Ventrals large, inserted just in front of dorsal. (i) Pseu- dobranchiae small. Thaleichthys albatrossis (Jordan and Gilbert) Characters: (a) D.2, lO; A.l, 20; scales 75. (b) Mouth large, lower Jaw heavy, strongly projecting. (c) Opercle with concen- tric striae. (d) Caudal moderate, well forked. (e) Dorsal high, anal fin low, long; ventrals long and pectorals moderate. (f) Ventrals inserted before dorsal. (g) Scales small, decid- uous, those on the back are still smaller. (h) Lateral line distinct. (i) Tongue with moderate teeth, anterior 2 to 4 small hooked canines. (3) Upper jaw with small sharp teeth similar to those in lower jaw, none of them canine like. (k) Small teeth on palatine and pterygoid. III. Genus Spirinchus Jordan and Everman External characters: (I) Body comparatively deep and compressed. (II) Head rather short and deep. (III) The maxillary broad, short, its edge strongly curved, extending to Opposite posterior margin of pupil. (IV) Mandible projecting. (V) Fins high. Spirinchggpthaleichthys (Ayers): characters: (a) D.9; szar-cely vi 81 translucent . :e;'.e:1t flav t: Eris: 01 l: External c‘r A.14 to 16; scales 55 to 58. (b) Teeth weak, maxillary teeth scarcely visible. (0) Olivaceous, sides silvery and somewhat translucent. (d) A weak and feeble species, its flesh of ex- cellent flavor. (e) Pacific coast from San Francisco northward to Bristol Bay in Alaska. IV. Genus Allosmerus, Lockington External characters: (I) Body elongate and compressed. (II) Head rather long, somewhat pointed, maxillary extending past pupil. (III) Lower Jaw projecting. (IV) Maxillary narrow and somewhat convex. (V) Outline of both Jaws nearly straight. Allosmerus annenuatus (Lockington): Characters (a) Eyes large. (b) D.lO; A.l5-17; P.1l; Scales 65. (c) Teeth on tongue strong, but small; teeth on maxillary conspicuous. (d) Front of both Jaws with rather strong teeth; palatine teeth variable, usually strong. (e) Fins low. (f) Pectorals not reaching ventrals, ventrals not reaching anal. (g) Greenish dorsally sides silvery. V. Genus Osmerus (Artedi) Linnaeus External Characters: (1) Body elongate and compresseda (ID) Head long and pointed. U“) Mouth wide, the slender maxillary extending to past the middle of the eye. (“0 Lower Jaw pro- Jecting. CT) Preorbital and suborbital bones narrow. (VI) Maxillary and premaxillary with fine teeth, lower Jaw with small x .ama> Seaweed «AQHmOBHEV KMREOS mbmmaamo .quzm z<0§m2< Ema .H m--DwH.m 2921‘s, which a strong, fang-1: mer, palatin- ra'ers are lon. Sales large, 51211, about I: 112g. (X!) Pyl: usheru 3°13; v.(5; sea anal WO/seve W318. (e) E a; .. 0...é the EC AC; LI‘Qnt 0" .3. “JOIQ D( l . (‘3) ,- Szaw _ es Cece“ 3;: +~ “Ce Ven teeth, which are larger posteriorly. Own Tongue with a few strong, fang-like teeth, largest at the tip. the Hyoid bone, vomer, palatines, and pterygoids with wide set teeth. (an Gill rakers are long and slender. (JO Branchiostegal rays 8. (31) Scales large, loose, 60 to 70 in the lateral line. can Dorsal small, about midway of the body, over the ventrals; anal rather long. (m Pyloric caeca small, few. Osmerus dentex, Steindachner; Characters: La) D.lO; A.l3; v.8; scales 66. (b) Eyes large, two—thirds langth.of snout. (c) Maxillary reaching posterior margin Of eye, its length 5 times in distance from tip of lower Jaw to dtxrsal. (d) Height of dorsal one-half the length of head; height of anal two/sevenths; pectoral shortish, reaching halfway tm>ven- trals. (e) Back pale olive, scales edged with darker. (IV Sides above lateral line purple, changing below to blue, and then to violet and gold. Osmerus mordax (Mitchill), American smelt (Fig. 1): Characters: (a) D.lO; A.l5; P.13; scales 68. (b) Body rather long and slender. (c) head large, with large mouth, and strong— er teeth than in the other species of the genus. (d) Small teeth along the edge of the maxillary; strong fang—like teeth on tongue and front of vomer; cardirorm teeth on palatines, pterygoids, and hyoid bone; mandible with moderate teeth, its tip proJecting. (9) Maxillary extending to a little beyond middle of eye. (f) Scales deciduous. (g) Dorsal fin rather posterior, in position and the ventrals under its origin; lower fins moderate, none acting the he than; on SlCE 113.15. 0 8:8 r1: zical, elongat :; upvard curt respercle; (: Largest on tr. at the upper 3:95 on the 3 color aoove , P323 6-11, C REST-1y lor. A: 3“va . .‘c‘ilostc x L..- _ s., v I NL“ e1- 0 s ’ is,» 'J IO reaching the next behind it. (h) Transparent greenish above, silvery on sides. (1) BOdy and fine with some dark punctula- tions. Osmerus sergeanti Norris; Characters: (a) Form ellip— tical, elongated and section oval; (b) Lower Jaw proJecting, with an upward curve; (c) Scales on all the gill covers largest on preOpercle; (d) Five large recurved teeth on the tongue, the largest on the extreme point, two of the same kind on the front of the upper Jaw; (e) No teeth on the vomer, a patch of small ones on the palatine bones and maxillaries. (f) Silvery steel color above, with light greenish reflections. (g) Branchial rays 8-11, 0 20; P 11; V 8, A 15; (h) Tail forked, upper lobe slightly longer.. Osmerug eperlanus: European species. VI. Genus Hypomesus Gill External Characters: (I) Body rather elongate, moderately com- pressed, covered with scales of moderate size; (II) Bead rather pointed, and the mouth moderate; (III) Lower Jaw proJecting; (1V) Teeth minute, on Jaws, vomer, palatines, pterygoids and tongue. (V) Ventrals inserted directly under middle of dorsal, and they are midway between eye and base of caudal; (VI) Branchiostegals 6 to 7. hypomesus pretiosus (Girard): Characters: (a) D.10; A.15; P.1a; v.8; Scales 70. (b) Fins low, the longest dorsal ray 8 in length without caudal; (c) Pectorals scarcely reaching ilfway to ven‘. olivaceou "A... U .. :usn', slight]. H'.”JO:F iliernal cnar II: Vertebral] WEIRD“; ¢-. ‘ nhm well u grin? mgr ‘ 11,5 ll halfway to ventrals, and the ventrals not reaching vent; (d) Light olivaceous above; (e) A silvery band along the lateral line. Bypomesus olidus (Pallas): Characters: Scales 56 to 60. (b) The dorsal fin higher than in Hypomesus pretiosus, the longest dorsal ray 6 in length of body; (0) Pectorals reaching 2/3 the distance to base of ventrals. (d) Coloration dusky, slightly translucent. Hypomesus Japonicus: found in Japan. VII. Genus Therobromus Lucas ‘l’o External characters: (I) Similarfithe genus, MeSOpus. (ED Vertebral formula 26 precaudals, 22 caudals, plus 1 hypural. Therobromus callorhini Lucas: Characters: (a) Chondro- cranium well developed: (b) Superior maxillary edentulous, pointed teeth on vomer and anterior part of palatine. (0) Lower Jaw very deep. (d) Pointed teeth on dentary. (e) Artic- ular well developed. (f) Vertebrae simple, anterior but very little shorter than the posterior; centra not sculptured, but bearing many fine longitudinal ridges. .NMB- Iherobromus callorhini is known only from skeletons and ‘bones.found in the stomachs of fur seals. MATERIALS AND METHODS 12 A nu")3 fie comercial :ichigan. and and Wildlife: Specinens for The 8: ways: (I) Boi and ammonia, )4) Use of d6 The I study: (I) B: monia, (3) In ti beetles prov eton is deli a: ushes wi th Period of 7 Part of body admit age 0 f Tn: -8 method ‘ r . °P this stu: MATERIALS AND METHODS A number of adult smelt for this study were taken from the commercial catch at Little Bay de Noc (February, I958), Michigan, and they were shipped to the Department of Fisheries and Wildlife, Michigan State University, East Lansing, Michigan. Specimens for this study were taken from this collection. The smelt's skeleton was prepared in the following ways: (I) Boiling the fish in the water, (2) Use of trypsin and ammonia, (3) Staining the skeleton with alizarin red, and (1;) Use of dermestid beetles. The following three methods were inadequate for this study: (I) Boiling the fish in water, (2) Use of trypsin and ammonia, (3) Staining with alizarin red. In the preparation of a skeleton, the use of carpet beetles proved to be the most useful method even if the skel- eton is delicate and bones are of membranous nature. The fishes with a label are left in the "Insect colony" for a period of 7 to IO days, and the beetles eat all the fleshy part of body and clean almost every piece of bone. The main advantage of this method is that the bones remain articulated. This method was very successful in the preparing of the skeleton for this study. 13 DESCRIPTle DESCRIPTION OF OSTEOCRANIUM OF THE SMELT (OSMERUS MORDAX) 114. l5 «Ndmroz mbfiflimog X N .BmH> A<fima¢4 .aqmzm HEB mo AQDMm .N amath 1? X N RMH> damaj .lxaqmoz msxmsmo. Hausa mma so 442mm .n amsmHa 18 19 axammoz mnmsamo, .aqmam mma so .m, .qqaxm so and: Emma so sommm< anamz 3: EDGHm 20 il ‘ ( 1.41 ‘) 1V. DESCRIPTION OF OSTEOCRANIUM OF THE SMELT (OSMERUS MORDAX) Olfactory Region Cartilage bones: Paired proethmoids (Fig. 2. PE), and unpaired ethmoid (E). Dermal bones: Paired prefrontals (PF), vomers (V), and nasals (N). The proethmoids (Fig. 5. PE): They are composed of fragile, cancellous endochondral bones. They are situated on the dorsal side of the vomers and are very obvious from the dorsal view. The fused proethmoids and the vomers are encased dorsally, anteriorly and laterally by cartilage continuous with the platnum ethmoidale. The proethmoids are exclusively sup— ported by the vomers and poateriorly are attached to the median ethmoid bone. The ethmoid (Fig. 5. E): It is a square shaped bone which lies medially with the vertical posterior edge perpen— dicular to its ventral edge. It is thin and sometimes over- looked. Ventrally it flares anterolaterally on either side of its median notch, which conforms with the underlying vomers. The prefrontals (Fig. 2. PF): They are poateriorly placed, remote from the ethmoid and vomers, leaving a long nasal fossa anteriorly. They have the same appearance as other membrane bones. Each is fused to the lateral border of the frontals. ')1 22 g§§_vomers (Fig. 5. V): They cannot be seen from the dorsal side, although their position is quite obvious from the ventral side, if the lower jaw is removed. They are thin, flat, paddle-shaped bones underlying the proethmoid, and overlapping the anterior and of parasphenoid ventrally. A pair of strong canine teeth is present on each vomer. Vomerine teeth are im- portant in the ayatematics of the family, Osmeridae. The nasals (Fig. 5. N): They are long, slender incon- spicuous bones attached to the corresponding frontals. They are very similar in appearance to the frontals, are situated laterally to the ethmoid, and are connected anteriorly with the proethmoids and posteriorly with the frontals. Orbital Region Dermal bones: Paired lacrymals (Fig. 2. LA), suborbitals (SB 2-4), suborbitals (SB 5-6), supraorbital (SO 7), frontals (F), and sphenotics (SP). The circumorbital bone§_(Fig. 2. LA, SB 2—6, SO 7): All the bones of the circumorbital series are arranged more or less ring-like around the eye. They are all flat, surmounted by a bony tube. Suborbitals 4 and 5 (SB 4-5) show a little evidence of fusion. Suborbital 6 (SB 6) is reduced to a bony piece, which is often white. Supraorbital 7 (SO 7) is attached h to the edge of the corresponding frontal andAlaid horizontally parallel with the prefrontals. z3 .BmH> Afimmoa .lxaomoa momaamoa sqmam she so qaogm .m mmooHa 24 Vomev (‘0 premaxiHa (PM) onelk‘fho)d (p5) efhmofd. (E) nose! (N) dotsal tonTeneHe ( DFO) fvcml a) (F) panel’s) (P) supva occipital 5X 25 (A) A Samoa mommzmoa x N as; hammoo .sqasm was so qaoam .c “423wa no 7.5 (B) .y, 3.))»3, 4.. A“. via: of ti bital :0 t”: ( olg U““Gn 3V». ”331e+ 26 The frontal§_(Fig. 5, F): They make the roof of the brain cavity and are Joined anteriorly with the ethmoid and the proethmoids. Posteriorly they are attached to the parie- tals. A fontanelle is found between the frontals, although they show a suture at the anterior and posterior ends. The sphenotics (Fig. 2. SP): They form the side walls of the cranial cavity, Join pterotics poateriorly and the or- bital region anteriorly. Otic Region Cartilage bones: Paired pterotice (Fig. 2. PTO), epiotics (EPT), exoccipitals (E0), prootics (PRO), and unpaired supra- occipital (SOC). Dermal bones: Paired parietals (P), posttemporals (PT), and supracleithrum (SOL). The pterotics (Fig. 2. PTO): Anteriorly they attach to the sphenotics and ventrally with the hyomandibulars. Their prper portion contributasto the surface of the skull externally sued to the vault of subtemporal fossae internally, within which ‘they fuse with the lamellae of the epiotics. Ven- ‘trolaterally, they curve around the horizontal semicircular ca- nals, rejoining their upper portion within the fossae, thus cunnpletely enclosing the canals,1and forming the other margin of the fossae. The epiotics (Fig. 4.): They enclose the posterior 27 semicircular canals. They are Just below the pterotics and poateriorly attach to the Opercular bones. It is assumed that the epiotics. fuse with the supraoccipital dorso-mesially, with the exoccipitals ventrOposteriorly and also ventro—mesially within the subtemporal fossae. The exoccipitals (Fig. h): They are not shown in the diagram. It appears that they fuse with the pterotics antero- laterally, with the epiotics dorsally outside, and laterally inside the subtemporal fossae. The exoccipitals Join mesially with the basioccipital. The prootics_(Fig. a.): They are situated on the ven- tral side of the braincase, completely invisible from the dorsal side. They are Joined by the parasphenoid, which is club-shaped poateriorly. Their posterolateral extensions form the antero- mesial curvature of the subtemporal fossa roof, and are Joined with pterotics and exoccipitals. The supraoccipital (Fig. 2. SOS): It is shield—shaped. There is a small median convexity. It seems that it has con— cave anterior border which conforms to the posteromedial margin of the posterior cnondrocranium fontanelle. The supraoccipital :forms sutures laterally with the epiotics and parietals. Pos- ‘terior to the sutures, it Joins the cartilage roofing of foramen nuagnum. The intermembranous spine of supraoccipital is present at; the posterior end of this bone. The parietals (Fig. 2. P): They overlie the posterior 28 part of the chondrocranial fontanelle, the upper portion of sphenoids, epiotics, and the supraoccipital. The right and left parietal Joins at the middle and both are Joined anterior- ly by the frontals. They are similar in appearance with front- als, smooth, slightly concave dorsally and more or less trian- gular. The post-temporals (Fig. 2. PT): They are lancet- shaped and the upper ends of these bones Join the epiotics. Both fuse at the dorsal side of the skull. The sub-temporals and supracleithrums are the intermediate bones between the skull and the pectoral girdle. The supracleithrums (Fig. 2. SOL): They are flat, paddle-shaped, with the anterior ends articulating with the under surface of the post—temporals, and the knife blade like posterior ends articulate with the lateral surface of the clei- thrums below. Basicranial Region Cartilage bones: Unpaired basioccipital (Fig. 4.). Dermal bones: Unpaired parasphenoid (Fig. 2. PS). The basioccipital (Fig. a.): it forms the roof and posterior wall of the myodome. The ventral wall is continuous behind with the conical, poateriorly concave centrum of the subsumed proatlas vertebra. Dorsoventrally, on each side, the basioccipital forms a suture with the ventromedial edge of the adJacent exoccipital. Z9 The parasphenoid (Fig. 2. PS): This is the longest bone in the skull of the smelt, and extends in the midline along the greater part of the ventral length of the neurocranium. At its anterior end, it is overlapped by the proethmoids and vomers. It constitutes a thick narrow strut of bone which skirts the lower edge of the vertical plate of the orbitosphenoid. At the posterior end of this bone, it widens abruptly to its max- imum width and forms a club-like structure. The club~shaped posterior end Joins with the prootics. A narrow groove is formed from the ventroanterior end of this bone which increases in its width from the middle part to the posterior end. Oromandibular Region Cartilage bones: Paired palatines (Fig. 2. PL), quadrates (Q), articulars (AH). Dermal bones: Paired metapterygoids (Fig. 2. MPT), entoptery- goids (ENP), pterygoids (PT), premaxillaries (PM), maxillaries (MX), supramaxillaries (S.hX), angulars (A), and dentaries (D). The palatines (Fig. 2. PL): They are dentigerous, rod- like and lie underneath against the ventral side of the entOp- terygoids. The anterior half of these bones have canines of variable number and size. Th3.quadrates (Fig. 2. Q): They are more or less tri— angular bones. Anteriorlyir they are flat and fan shaped, pos- teriorly they are produced in a long, thick, handle-like knob. 30 At their anteroventral angles, they bear the condyles which articulate with the notch in the angulars. Dorsally, the mesial surfaces of the quadrates are applied to the lower lateral sur- faces of the posterior ends of pterygoids. The articulars (Fig. 2. AR): They are small, slender bones, almost united with the dentaries, and posteriorly fused with the angulars. The metapterygoids (Fig. 2. MT): They are broad, flat bones, andfi are almost rectangular in shape. The dorsOposterior and dorsoanterior anglasof these bones form the chief point of articulation with the hyomandibulars. The symplectics Join the hyomandibulars and the metapterygoids posteriorly. Dorsoanter- iorly, the mesial surfacesof the metapterygoids are applied to the posterior lateral surface of the entopterygoids. The right half of the metapterygoids borders on the dorsal edge of the symplectics. Th; entOpterygoids (Fig. 2. ENT): They are similar in appearance to the metapterygoids. Their mesial surfaces are attached above the lateral surface of the anteroventral corners of the pterygoids. Their lateral surfaces are applied to the mesial surfaces of the anterior parts of the quadrates. The entopterygoid and the pterygoid are almost fused together, their respective areas being only partially distinguishable. On their ventral sides, mesially, there is a series of teeth present. 31 The pterygoids (Fig. 2. PTO): They are almost fused with the entopterygoids. They narrow gradually towards their anterior ends. The homology of the pterygoid is confused. The pterygoid and the entopterygoid of the fishes represents only the pterygoid in the mammalian skull. The premaxillaries (Fig. 5. PM): They are short, slender and dentigerous bones, most anteriorly situated on the upper Jaw. They meet in the middle of the anteriormost part of snout. Teeth are variable in number and size. The dorsal edge of premaxillary is attached to the ventral edge of maxillary and overlaps the vomers. The maxillaries_(Fig. 2. EX): They are the main bones of upper Jaws, and are strongly toothed. They have large knobs at the anterior ends which fit into distal concavities of the submaxillary cartilages. This knob—like condyle is the anchor and pivot of the maxillaries. Below the knob, each maxillary sends mesially a slender rod, which approaches a corresponding rod from the other maxillary. Except at their anterior ends, the maxillaries are thin and flat and have a broad ascending crest much like that of the dentary. The supramaxillaries (Fig. 2. SMX): They are situated dorsolateral of the posterior half of the maxillaries. They are more or less hammer—shaped and some fusion has occurred with the maxillaries. They are glassy in appearance and almost transparent. The ventral side ofAsupramaxillaries attaches to 32 the the dorsal side of the posterior half offimaxillaries. The angulars (Fig. 2. A): They are the small bones situated at the knobs on the posterior parts of dentaries. They have a dorsal notch here for the articulation with the quadrates, and opposite to these, the ventral notches into which the dorsal edges of articulars fit. They almost fuse with the dentaries. The dentaries (Fig. 2. D): They are the largest bones in the mandibles. Each curves mesially and anteriorly, to form the symphysis with its fellow of the opposite side. The den- taries send dorsally the flat, broad, ascending ridges - which possess the strong teeth. The teeth bearing borders of den- taries and the posterior knobs are opaque, while the remainder of these bones are translucent. Hyoid Region Cartilage bones: Paired hyomandibulars (Fig. 2. HM), symplec- tics (SI), interhyals (Fig. 7. IE), epihyals (EH), ceratohyals (CH), hypohyals (HH), and unpaired basihyal (BH). Dermal bones: Paired operculars (OP), preoperculars (POP), suboperculars (SOP), interoperculars (IOP), branchiostegals (BS), and unpaired urohyal (UH). The hypmandibulars (Fig. 2. HM): They are very irregu- lar bones in both structure and shape. They articulate anter- iorly with metapterygoids and are attached below to the sym- plectics through cartilage. They consist of the thick swellings 33 .ZmH> ddmmoa anmoa m: m mumov Bdmzm Mma ho EflBmMm Ah. ma . h .9 .“Wmmnw&¥» 7.0.; Fe treat ”mafia... {gnaw .0. _m..r.eFo>Aom .5295 I .m . on .mxfirfmm tarmac _ on»: 1150.5 \\\ _cx:uwog 35 . .SHH> 133mm: .anmoa mommamoa Seam are so 5% Ema £32 Bore .w mmeH.m 36 37:3,: Erin—m 333050 37 of bones with thin flanges extending on either side, anterior— ly and posteriorly, respectively. The anteriormost strut at- taches to the sphenotic and forms a triangular piece of bone. From its anterior angle another triangular bone hangs down laterally which attaches to the metapterygoid and symplectic. There is a distinct gap between hyomandibular and preopercular. The symplectics (Fig. 2. SI): They fit in the grooves on the dorsal surface of the posterior extension of the quad- rates. The anterior ends are inserted between these extensions andfifan-shAped part of quadrate. The interhyals (Fig. 8. IH): They are small, somewhat cylindrical, connected at one end with the cartilage between the hyomandibulars, symplectics and metapterygoids, and at the other end with the upper end of the epihyals. The epihyals (Fig. 6. EP): They are thick, massive, somewhat triangular and their spices are directed dorsolater- ally towards the interhyals. Their bases are broadly articula- ted with the posterior ends of the ceratohyals. The ceratohyals (Fig. 8. CH): They are broad, and lateroposteriorly Join the epihyals. The dorsal head articu- lates with the upper hypohyal, the ventral head with the lower hypohyal. The hypohyals (Fig. 6. HH): They have two parts, upper hypohyal and lower hypohyal. The upper articulates at one end with the ceratohyal and other end with lower hypohyal. The lower hypohyal is more or less V—shaped bone. 3a ..».Ji..u x m .zmH> damaged .Axaomoa mommsmo. samam was so aqosm some mmaqsonamomem was .m HmeHm 39 40 The basihyal (Fig. 7. BH): It is a massive, thick and dentigerous bone. It takes the position of the tongue in the mouth. Teeth are strong and curved. The urohyal (Fig. 7. UH): It is a flat, broad, hori- zontal plate surrounded by the hypohyals laterally, basihyal anteriorly, and basibranchial posteriorly. The branchiostegals (Fig. 2. BST): They consist of five pairs of flat, curved bones, which are arranged like the leaves of a book in an ascending manner from the anterior to the posterior, on the ventral side of the skull. Most of them are slightly produced anterodorsally and articulate with the hyoid apparatus. The preoperculars (Fig. 2. and 9. PO): They are sickle- shaped and overlap the anterodorsal surface of hyomandibulars, the posterior end of quadrates, symplectics, the interhyals, the upper lateral surface of the interoperculars and anterior edge of operculars. The interpperculars (Fig. 2. IO): They are more or less triangular, with slightly incurved upper edges. They overlap the anterior ends of suboperculars and are overlapped antero- laterally by the preoperculars. The suboperculars (Fig. 2. SO): They have the charac— teristic semilunar shape and the anterior ends are overlapped by the posterior end of operculars. The anterior margin of suboperculars overlap the posterior end of interoperculars. 41 The operculars (Fig. 2. OP): They are very thin, almost glassy in appearance and transparent. The posterolateral ends overlap the supracleithrums, cleithrums and postcleithrums of pectoral girdle. The lower edges overlap the suboperculars. Branchial Region Cartilage bones: Paired pharyngobranchials (Fig. 7. PB), epi- branchials (EB), ceratobranchials (CB), hypobranchials (HB), and unpaired basibranchial (BB). The pharyngobranchials (Fig. 7. PB): There are two pairs of pharyngobranchials. The ceratobranchials (Fig. 7. CB), and the epibranchials (Fig. 7. EB): They are thin, long, cylindrical bones. The upper end of epibranchial and lower end of the ceratobranchial are Joined with articular heads. The articular heads are thick :hile the opposite ends are thin. The fifth epibranchial is not evident. The hypobranchials (Fig. 7. HB): These consist of three pairs of osseus, comma—shaped bones, quite adJacent to the basi- branchials. The fourth hypobranchial is found in some ' species, but is absent in the smelt. The basibranchials (Fig. 7. BB): These are three strong, cylindrical bones, which articulate end to end and arrange in a linear fashion. They are unpaired, and lie in the midventral line of the pharynx. The first basibrancnial is a curved rod #2 of bone lying between the hypohyals and extending anteriorally beneath the basihyal. The second basibranchial is strong, longgc cylindrical with the several teeth of almost equal length. The third basibranchial is shorter than the second, and has a broad articulating surface at the posterior end and is pointed at the anterior end. COMPARISON OF THE SMELT' S SKULL WITH THE SKULL OF THE SALMON 43 1+4 ¢ new. .Nmowmm$ MHBhfl has: again 2% 9.3% so deem .OH mmbéHm 45 (s E. . . L be... peek he. .. 1“ 46 D . .I'e-l—IT.. .Hmoammw mmam< as; 1:5on ..mm 9.3% so .385 .HH mmeHh 47 48 . ~ . ! wilt“. x N as: anaemia :xaioa mommzmos Seam ”a; so .338 .NH mmDGHm 49 50 NN .saH> gammoa .kxeas a mommZmov eqmam was so aaoam .ma amooHs 51 Foreman F SOC COMPARISON OF SMELT'S SKULL WITH THE SKULL OF SALMON The parietals (Fig. 10. Pa) of the salmon (Salmo salar) are small, ridged and subarcuate, separated by the whole width of the broad supraoccipital. They articulate with it and also with the corresponding frontal and epiotic. The parietals (Fig. 12. P) of the smelt (Osmerus mordax) unite in the mid- dorsal line. Anteriorly each is attached to the frontal and posteriorly with the supraoccipital. The frontals (Fig. 10. fr) of the salmon are large and strong. They meet to form the sagittal suture in their posterior half, but further forwards a smooth ridge of cartilaginous skull separates them. The frontals (Fig. 12. F) of the smelt are flat, and form a sagittal suture posteriorly. Anteriorly they meet with the proethmoids and ethmoid as well as slightly touching each other. There is a long fontanelle in the center portion. The vomers of the salmon are oblong and thick in front, with a sharp keel on the anterior portion, between the paired ethmoids. They bear the sharp recurved teeth. These bones underlie the proethmoids for a considerable distance. Th2 vomers (Fig. 13. V) of the smelt are in very much the same posi- tion as in the salmon. Each vomer possesses a pair of teeth. The paragpnenoid (Fig. 10. par) of salmon is of great length. This bone is large, long, leaf-like, with descending laminae and split in front. It is upwardly keeled in front, 52 53 downwardly keeled behind, and flattened in the middle. In the smelt, it (Fig. 12. P8) is the largest bone of the skull and upwardly keeled in front and downwardly keeled behind but not flattened in the middle. The suborbital bones (Fig. 10. la, So 2-5, dsp, s0p) of the salmon are thick and strong-rimmed where they lie more or less in a ring about the eye. In the smelt, they (Fig. 12. LA, SB 2—o, SO 7) are weak and border almost three-fourths of the orbit. The lacrymal is quite long, situated ventroanter- iorly while the remaining bones are arranged in the semi-cir— cular fashion about the ventral and posterior margin of the eye. The premaxillaries and the maxillaries (Fig. 10. pmx, -mx) of the salmon are dentigerous. The premaxillaries are the broader an” more massive of the two. They have a region where the structure is peculiarly sponge—like and tubuliferous. The smelt has premaxillaries, maxillaries and supramaxillaries (Fig. 12. PM, EX, & SAX). The premaxillaries as well as maxillaries are dentigerous although the maxillaries bear the weaker teeth. The maxillaries in the salmon are concave where they are overlapped by the premaxillaries. They send inwards a concave facet for the articulation with the palatines, are rod—like in their dentigerous portion, and flatten out below, especially on the upper edge which is overlapped by the Jugal (Fig. 10. Ju). The maxillaries in the smelt have large knob—like structures at their anterior ends which fit into the distal concavity of the submaxillary cartilage. 54 The dentaries (Fig. 10. dn) of the salmon bear teeth which are strongly hooked. They are the principal bones of the mandibles, which are turned up so as to fit into the anterior end of the snout, giving the peculiar characteristic of the salmon's face. The dentaries (Fig. 12. D) of the smelt also bear teeth which are sharp and pointed upwards. The posterior half of these bones is very wide but they narrow anteriorly where they meet the fellow of the other side. The lower Jaw is slightly longer than the upper jaw. In the salmon, on the angle of each mandible another splint is found, the angular (Fig. 10. an), which is small and rough. In the smelt the angular (Fig. 12. A) is very small, almost at the same location as the angular in the salmon. The articulars (Fig. 10. art) in the salmon are fairly big and occupy almost one half of each mandible, while the arti- culars (Fig. 12. AR) of the smelt are quite small and located at "1" $4 the Junction of angulars and posterior knobs of dentaries. The preoperculars (Fig. 10. preo) of the salmon are quite membranous; they have the usual falcate form, are furrowed in a radiating manner by mucous glands; their attachments are by their anterior edges, above the posterior edge of the hyomandi— bular and below that of the quadrate. In the smelt, the location and structure is the same, except that their posterior edges overlap the anterior edges of operculars. The operculars (Fig. 19. 0p) of the salmon are large and 55 subquadrate. They are elegantly marked with growth-lines, and they articulate with the hyomandibulars by ball and socket joints. The operculars (Fig. 12. GP) in the smelt are glassy and trans— parent; anteriorly, they articulate with the hyomandibulars and ventrOposteriorly overlap the suboperculars, cleithrums, and postcleithrums. They show no markings of growth-lines. The suboperculars (Fig. 10. app) of the salmon are some— what below the operculars; they are subfalcate, broad in front, very thin and elegantly marked with growth—lines. The subo;er- culars (Fig. 12. SO) of the smelt are semi—lunar shaped and there is no trace of growth-lines. The operculars overlap the upper edge of suboperculars. The subOperculars overlap the cleithrums, scapulae and coracoids of pectoral girdle. The interopergulars (Fig. 10. iop) of the salmon are ear—shaped; their narrow ends passing behind the preOperculars are very thin. They are marked concentrically and radially by growth—lines. In the smelt (Fig. 12. 10), these bones are small and are overlapped by the edges of preoperculars, and show no trace of growth—lines. The hyomandibulars (Fig. 10. hyom) of the salmon are broad, flat bones, which articulate anteriorly with the pter- otics, but partly also with the sphenotic elements of the otic capsules. Below they are connected with the slender symplectic bones and form the cartilage connecting the entopterygoids and quadrates. They support the rest of hyoid arch, consisting in succession of interhyal, epihyal, ceratohyal and hypohyal bones, 56 with the median tooth-bearing basihyal. In the smelt, the hyomandibulars (Fig. 12. HM) are peculianyshaped bones with the anterior triangular pieces attaching to the posterior pieces by a narrow joint. They are almost in two pieces in the smelt. The symplectics (Fig. 10. S!) of the salmon have a real suspensorium with the hyomandibulars, and they are fused with the anterior margins of the quadrate and the metapterygoid bones. In the smelt, similar attachments of symplectics, quadrates and metapterygoids are found. The comparison of smelt and salmon‘ skull bones is summarized in tabular form below. 57 .hpmpcmo amp mo omom moahomeQOmmop haco mmm>oo cam HHwEm mHaHmL .HHmSm .pmxooz pom mam mosh .qu swam: camp he .mcoa hapnmaam ma qu moaoa one .muam Hasxm mud on comaawmaoo ca whoa use gamma mam gamma .mSOAoprcoc paw oxaa pox .maeeas map as pews ewes .oco poapopmoa mzp um cmopn has macnmmapcmp .pmawmm m>mocoo .msoamwapcmp pad HHme .CHQB .mmama manamh ma Haemaoma .onEHa can» 0cm xmmz .maeeas mes ea emcmppwaa pox .pcmmmpd ohm gamma .Emnp cooapmn 2H hoamaow mwhma mhm> m m>m£ use mam; mao>apqswqeoo .obdm Hmmaoc 03p Sosa pampa>m opasv zaama Imma puma mega .wcoapm hapamh .&xmpmoe mammEmov pamam z Eddm mo Adsmm .zsmpcoo no when moved: map mcaam>oo 0cm mwawa zapamm .mmSOh cam HHwam .oomh m.coaamm can no mamnm amH450mQ map m>aw chm poxoos mHmCOpr one gnome .msommwapcmb chm oxaa pom .Boamn pso pocmppmaa cam muoamwapmmu .Umddhm masocoo .msoamwapcod paw chomp .m>ammm2 .xoanu 6cm cossaa whoapw .maeeaa mes ca swamppsaa .pcmmmmu ohm mumps .mmSQSm d An comaow chm mmamq .Hmpagaooo umAQSm an pmpmammom uwcoapm Asmamm oaHmmv coefimm mm% mBHB AADMm m.adm2m m0 zomHmdeOo H .02 wqm .ampcosa .Hmpoasmm econ go mama .HH .OH 58 .amasnaccm805£ Spas coacs mpmaasoo m man came who mpa was mgmnm CH amaswcmaaa .mmwnm Ca psaswcwanp mama no oaoz .coaamm one CH mm 05mm .pCHOq 3opawc a an oomam aoa unopmoa esp Op monowppm woman addsmcmaap m zaaoaampcw ..m.a .mpth 039 opca oHQHmH>HQ .mmcaalfluaomw wo whaxama Hmacwa cum cams Ismocoo ham adoflpdx cam HHmEm .mocHH unpaosw mum pSOQpHE chm cams Id: cmomn .mmmmflm amazauaamm .mmmaa;£pzoam mo mwcdxama mam usonpaa mocmpmmaam CH mmmmdw L$m¢wumpmoamw mamcoapmxma pH .Uaombpm IpQOpCo pew smaspapcm505£ Spas COHpomccoo was dam Show opwoawh .oqmnm Ga awasmcwHAp hHmQOApm .amasnaccmaohfl map spa: adaaomCoamSm Hmma mm: .oaponmpq map spas mamoahop use mmpmasoaphw .mhon away cmosm .pcmmwpg mam mochauflpzoam pcm wmamnwlawn .mmhaa nupaoam Spas powama AHPCmmmHm was pzoah ca chomp .mpmoamgpsm .mmcHHISpsosm yo mwcHMama spas opmasmdthm mam mmpmq .omamflm mpmoamy ma pa «.Upcoog H .02 m4m soasopmom .Amonxqv mapmpam> amends .Q .3ma> Loammpmom .Aaznmu appease» Hmoaqmp 4 .0 a .m .3ma> poaampmom .ammap papa: .4 .AX¢QmOE mbmmsmou admsm mma mo Mdmmmamm> .iH mmwam 61 he ("6‘ zygapo 951 5601.176) newal arch (NA) \ % ceh’fvu m (C) cehfflfl cana\ (CC) new a 1 spf'ne Rf..— u'wnfevmo scum? bone Ceh‘hrum cenTral canal Para popkyses (PA. PH) é—————r|'bs (R) mews) spine (N5!) neural arch mfev muscular bong (1M3) cehfvum Pavaporhyses Rib s (Q) <— heuYal spine neuval aYch “swell canal 7‘va Ivs’apoph ses ,______.. cewh'a‘ CahaI 7 am“ Zva'aporkvses Rhee "ma! arch (1 ae‘mal 5P3“€(H.SP.) Ix. ’ id c..- r 7. I?! .l. V. 02 mmB X A5230: mammzmo, Sham m0 :Hm A mamqmzoo Ema .mH mmeHh 63 DESCRIPTION OF VERTEBRAL COLUMN OF THE SMELT (OSHERUS MORDAX) The vertebral column is completely ossified with.an aperture in the centrum.of each vertebra. It is divisible into an anterior or trunk region and a posterior or caudal region, together comprising about sixty-one to sixty-two vertebrae. The first forty-one vertebrae comprise the trunk region while the remaining twenty or twentyéone constitute the caudal region. The vertebrae from the trunk region possess pleural ribs while the caudal region vertebrae have the ribs fused to form.haemal spines. A typical trunk Vertebra consists of a cylindrical cen- trum (Fig. In, B and C) with deeply concave anterior and post- erior faces (amphicoelous), and perforated in the center by the narrow central canal (Fig. In). The edges of the centra area united by ligaments and the biconvex spaces between them are filled with the remains of the notochord. There are also articulations between the neural arches by means of small bony processes, theéygapOphyses (Fig. In, B and C). The low neural arch is attached to the dorsal surface of the vertebrae anteriorly by ligaments and posteriorly by ankylosis. To the ventro-lateral region of the vertebrae are attached by a ligament, a pair of long and slender pleural ribs ( (Fig. In. R), Which curve downwards and backwards between the muscles and the peritoneum, thus encircling the abdominal cavity. In the first two vertebrae they are 61L 65 attached directly to the centrum, the rest to short downwardly directed bones, the parapophyses (Fig. 1%. PA, PH), immovably articulated by broad surfaces to the centrum. At the Junction of the neural arcn with the centrum are attacned, also by fi— brous union, a pair or delicate inter-muscular bones tFig. 14. 1MB), which extend outwards and baCKwards in the fibrous septa between the myomeres. The first and second vertebrae bear no ribs. There are no ribs on the last 2 or 3 vertebrae of the trunK region. In all the trunk vertebrae the neural arChes are produced dorsally to form a spine. The caudal vertebrae have zni amphicoelous centrum, which is perforated in the center by a narrow canal. The outgrowths corresponding to the parapophyses are fused with the centrum and form part of the roof of the haemal canal, through which the caudal artery and vein run. In each caudal vertebra, the ribs are fused into a single arch, which is produced downwards and backwards into a haemal spine (Fig. 14. H.SP). The posterior end of the caudal region is curiously m0di- fled for the support of the tail fin. lhe ultimate centrum (Fig. 15), has the axis not horizontal, but deflected upwards, and following the last undoubted centrum is a rod—like structure, the urostyle (Fig. 21. UST), consisting of the partly ossified end of the notochorc, whichkas thus the same upward flexure as in the Dog fish (Scyliorhihus canicula). Therieural and haemal spines (Fig. l“. N.SP., H.SP), of the last two or three vertebrae 66 are very broad and closely connected with one another, and more numerous than-tithe centra: and five or six haemal arches are attached to the urostyle. In this way a firm vertical plate of bone:;is formed, to the edge of which the caudal fin rays (Fig. 21. CFR) are attached fan-like in a symmetrical manner. It will be obvious, however, that this homocercal tail fin is really quite as unsymmetrical in structure as the heterocercal caudal fin of the Dog fish, and since its morphological axis is constituted by the notochord, nearly all of its rays are, in strictness, ventral. DESCRIPTION OF DORSAL FIN OF THE Sl‘-.ELT (OSL’ERUS l'LORI‘.-AX) 68 .‘J I] 1}}v'ibllli \ , x .3 .4 r mot m2 -mmmou Eqmdm flfl r r _ .4 1 Km m0 ZHh 44mmom .OH mmeHm 68 DESCRIPTION OF DORSAL FIN OF THE SI-ZELT (OSI‘ERUS IR'TORDAX) The total number of dorsal fin rays varies from IO to 12. The number of branched rays is variable from 8 to IO. Each dorsal fin ray is supported by a triple set of pterygiophores. The dorsal end of a pterygiOphore fits under the base of the dorsal ray. There are small nodules of cartilage forming the third series of radials which are situated below the dorsal fin rays. These radials are conn- ected to the second series. The proximal series consists of slender bony rays - the interspinous bones, lying in the median plane, between the muscles of right and left sides, and more numerous than the myomeres of the regions in which they occur. The dermal fin rays (Fig. I6), which lie in the subs- tance of the fin itself: are slender bones, joined like the antennae of an'arthrOpod, and mostly branched in the sagittal plane. Each is formed of distinct right and left pieces in close contact fun the most part, but diverging below to form a forked and dilate end, which fits over one of the cartila- ginous nodules. ' The second dorsal or adipose fin has no bony support. It is one of the significant characteristics of the family, Osmeridae. 7O DESCRIPTION OF PECTORAL GIRDLE AND FIN OF THE SMELT (OSMERUS MORDAX) 72 .EE gflmaa . flame: massaged Shaw was .8 Es nfioaomm 52 Engage .flpfiom .Eooamoo and .NH mmDuHh 73 >2 c; Sea 1108 $83 $.0umyoo DESCRIPTION OF PECTORAL GIRDLE AND FIN OF SMELT (OSMERUS MORDAX) The pectoral girdle consists of three bones, the scapula, the coracoid and the cleithrum. The scapula (Fig. 17, SOP), is situated dorsally to the glenoid fossa which is the articulating surface Oprectoral fin. The coracoid (Fig. 17, COR) 13 situated ventrally to glenoid fossa and the mesocoracoid is situated above the coracoid and anterior to the scapula. Ex- ternally to these is formed a large investing bone, the clei- thrum (Fig. 2, CL), extending downwards under the throat. Dor— sally it is connected with the supracleithrum (Fig. 2, SOL), and the supracleithrum is connected to the forked post-temporal (Fig. 2, PT), one branch of which articulates with the epiotic and the other with the pterotic process. The postcleithrum has an at- tachment with the postero-dorsal side of cleithrum. The post—temporal, supracleithrum and the cleithrum form a chain of essentially long narrow bones which attaches the pec- toral girdle to the shull. The postcleithrum (Fig. 2, POL), is smaller than the cleithrum and it is a spindle-shaped bone placed at an angle with its longitudinal axis directed postero- ventrad. its anterior end lies underneath the cleithrum while the posterior end is embedded in muscle underneath the pectoral fin. The coracoid is a roughly triangular bone with the base at its posterior end. The apex of the triangle at- taches to the cleithrum by a tough ligament. The scapula is a 74 75 small, subquadrate bone with a deep notch on its ventral border. The anterior half lies underneath the cleithrum and is fused to it. The radial bones support the pectoral fin rays. Radials as well as the coracoid and the scapula apparently arise as separate centres of ossification. The number of pectoral fin rays varies from l2 to 13. DESCRI PTIO‘” ' .1 OF PEI. VIC V -IN OF ‘I‘I‘E S*'EL r; T (051m --:.RUS MO ~ RDAX) 76 as: nausea Andaman. , and V 3an she no Ea 35mm and .3 ”ESE 78 >0 > F; EEC/mg horse 0 are...» :m 5 a» o~r>>£m .3 39b 7:. . a my fauwrrofia mm 79 4 plu'.(.1".1 a 33> 943593 . Ago: mbmnflfiov BHHEm Ema ho .0th 0H>Amm .mH gunk ”.9 80 DESCRIPTION OF PLLVIC FIN OF THE SMELT (OShERUS MORDAX) There is no pelvic girdle, its place is taken by a large, flat triangular bone, the basipterygium (Fig. 18, B. PTG); to its posterior border are attached three partly ossi- fied nodules, the distal pterygiophores (Fig. 18. TC), and with these the dermal fin-rays are articulated. The number of pelvic fin-rays varies from d to 9. 81 DESCRIPTION OF ANAL FIN OF THE S \ V J. iELT (OSMERUS EORDAX) 'x.ifiz.-ur.mm ~q Ib‘jfim s .5 ‘ ‘1' ~12 Ir 83 Van “wade: ws,-.,mum3 Sham was go fig 432 .8 ago: DESCRIPTION OF ANAL FIN OF THE SMELT (OSHEQUS'MORDAX) The total number of anal fin—rays (Fig. 20) varies from 15 to 17. The number of branched rays is variable. The number of pterygiOphores in the anal fin is 15 to 17. The anal fin rays are supported each by a triple set of ptery— . giophores. The proximal series consists of slender bony rays - the interspinous bones lying in the median plane, between the muscles. Their distal ends are broadened, and with them are connected the second series; to these finally are connected small nodules of cartilage forming the third series of radials. The proximal series of the radials are long and pointed upwards while ventrally they possess the broad articulating sur- faces. The second series of radiales are smaller than the first series, and are situated in between the first and third series. The third series of radiales are the smallest of the three and connect the second series to the anal fin rays. 85 DESCRIPTION OF CAUDAL FIN OF THE SFELT (OSEERUS E-fiORDALX) 87 I u .Il.<|| )r'slifi. .0HB<33<¢$N .959» 0:.an BLDG-b. A5343 89 :4 lawnmoa mammamoi do X N ZHm AdQD