Cyprinus Carpio </Emphasis> Linn

Proc. Indian Acad. Sci., Vol. 85 B, No. 5, 1977, pp. 351-363.

The development of the ehondroeranium of Cyprinus carpio Linn.

R. G. PASHINE AND V. B. MARATHE Department of Zoology, Institute of Science, Nagpur440001 MS received 29 April 1975; in revised form 20 September 1976

ABSTRACT

The common carp, Cyprinuscarpio Lian. has been studied for the development of the chondrocranium. A large number of early developmental stages of the embryos were fixed at regular intervals of time. The develop- meat of the cartilage has been traced from the serial sections which were cut at 10 micra. These sections were stained with Delafield's haematoxylin and eosin. Waxo model and graphic reconstructions were prepared. For some stages, bulk stained preparations were also made. Eleven stages have been investigated and described.

1. INTRODUCTION

NUSBAUM (quoted by De Beer 1) has studied the development of the skull of the carp, Cyprinus carpio, only so far as the Weberian ossicles al'e con- cerned. What little knowledge exists is, therefore, practically restricted to the posterior region. A perusal of the literature reveals very little information concening the structure and development of the chondrocranium of the common carp, Cyprinus carpio Linn., belonging to the family Cyprinidae. In order to fill up this lacuna, the development of the chondrocranium of this food fish has been studied.

2. MATERIALAND METHODS

A larger number of fertihzed eggs of Cyprinus carpio were collected from a local fish farm. The fertilized eggs were reared in the laboratory and a large number of stages were fixed at regular inte,vals of time. The fixatives used were 70% alcohol, 5% formalin, picro-formal and acetic-alcohoL The serial sections of the alevins were cut at 10 micra and were stained with Delafield's haematoxylin and eosin. The stages in which the bones had already developed, were decalcified and the bulk stained preparations were made by van Wijhe's technique) Wax model and graphic reconstructions were prepared in several cases.

351 B12--May 77 352 R.G. PASHINE AND V. B. MARATHE

3. OBSERVATIONS

STAGE 1: TOTAL LENGTH--3.73 MM (60 HR) (figure 1) The foundation of the cartilaginous skull has been laid down in the form of a pair of independent procartilages, the trabeculae (tc), measuring about 60-70 microns in length. The notochord (n) is well represented.

STAGE 2: TOTAL LENGTH--4.28 MM (66 HR) (figure 2) The trabeculae (tc) are cartilaginous and have increased in size extending upto about 90-100 microns in length. The parachordals (pc) are noticed as procartilages.

STAGE 3: TOTAL LENGTH----4"4 MM (69 HR) (figures 3 and 4) The trabeculae (tc) extend.further in the ethmoid region and anteriorly they join to form a small ethmoid plate (ep), extending for over 30 microns. The trabeculae and the parachordals together enclose a hypophysial fenestra (hf) which extends to over 300 microns. The occipital arches (oa) have appeared and extend to over 20 to 30 microns. The capsular cartilages (ac) are laid down in the anterior part of the auditoiy sac (as). The notochord (n) extends for about 100 microns into the hypophysial fenestra (hf). Meckel's cartilage (me), quadrate (qu), hyosymplectic (hs), ceratohyal (ch) and the first two branchial arches (ba 1-2) have appeared. STAGE 4: TOTAL LENGTH---4.52 UU (72 nR) (figure 5) The anterior end of the auditory capsule (ac) is better chondritied. An anterior basicapsular commissure (abc), connecting the anterior part of the auditory capsule to the anterolateral border of the pa:tachordal has appeared. The hyosymplectic articulates with the anterolateral side of the auditory capsule.

STAGE 5: TOTAL LENGTR--4"7 MM (81 I-IR) (figures 6 and 7) The ethmoid plate (ep) is slightly better represented. The palachordals (pc) extend behind to join the occipital arch elements. The quadrate (qu) has increased in size. The hyosymplectic (hs) is well formed and extends underneath the posterior part of the quadrate. The third and fourth branchial arches (ba-3 and ba-4) have appeared. The fifth inch (ba-5) is in proeartilaginous stage.

STAGE 6: TOTAL LENGTH--5"0 MM (90 rig) (figures 8 to 10) The parachordals (pc) have broadened at the posterior end. The lateral wall of the auditory capsule (rac) is appearing. Meckel's cartilage (mc), CHONDROCRANIUM OF Cyprinus carpio INN. 353

-(15

E P ~ep "k'nC /~r., -~ ctbe ctbc ~ -.

pc pc ...pc

,:." .~btt-s 1-1/

ep~ ~ 'h t% , f raC ( b~c '3u" ch bb-i s sh__.b,~ ~ I ? " (1.C pc pc E z.._g oa -rl I o.3 mrn.J bg.8

Figure~ 1-10. 1. Dorsal view of the chondrocranium of Cyprinus carpio, stage 1 (3.73 ram). 2. Dorsal view of the chondrocranium of stage 2 (4.28 ram). 3. Dorsal view of the chondrocranium of stage 3 (4" 4 ram). 4. Dorsal view of the visceral arches of stage 3. 5. Dorsal view of the chondrocranium of stage 4 (4.52mm). 6. Dorsal view of the chondrocranium of stage 5 (4" 7 man). 7. Dorsal view of the visceral arches of stage 5. 8. Dorsal view of the chondrocranium of stage 6 (5.0ram). 9. Dorsal view of the mandibular arches of stage 6. I0. Dorsal view of the hyoid arch and five branchial arches of stage 6. (Explanations for the abbreviations in figures are given in p. 363 ) 354 R.G. PASHINE AND V. B. MARATHE quadrate (qu) and hyosymplectic cartilage (hs) are better represented A small basihyal (bh) is noticed and it measures about 60 miclons in length• The head of the basihyal is broad. A small cartilaginous stylohyal (sh) appears between the ceratohyal and the hyosymplectic cartilage. All the five branchial arches (ba 1-5) are distinct. Thee is a cartilaginous first basibranchial (bb-1), supporting the first and the second pair of branchial arches.

STAGE 7: TOTAL LENGTH--5"4 MM (102 Ha) (figures 11 to 13) The ethmoid plate (ep) has increased in size and is continued behind as the trabecula communis (tcom). In front of the anterior basicapsular commissure (abe) a thin, lateral commissure (lcm) is formed. Between these two commissures, is noticed a trigemino-facialis chamber (tfc) through which

..: ep hb-1 bh ch ~com mc r'}P

'i 2: '. ~¢ c~ ~ du,~ ~, bvc ~ i

....--~,_~,-ep mcu . bh co

::"~ 1.cm +,+ hb-+ ~ cb-1

bp ifi/:::: i,

to.3 mm! 18

Figures 11-16. 11. Dorsal view of the chondrocranlurn of C. carpio, stage 7 (5"4 ram). 12. Dorsal view of the mandibular arch of stage 7. 13. Dorsal view of the hyoid and branchial arches of stage 7. 14. Dorsal view of the chondrocranium of stage 8 (6.0ram). 1~, Dors~ view of the mandibular arch of stage 8. 16. Dorsal view of the hyoid and branchial arches of stage 8. (Explanations for abbreviations in figures are giver in p. 363) CHONDROCRANIUM OF Cyprinus carpio LINN. 355 pass the V and VII cranial nerves. Posteriorly a small basivestibular commissure (bye) is noticed, which is not yet connected with the auditory capsule. The orbital cartilages (ore) have appeared as small cartilaginous rods, located between the trabecula communis and the auditoly capsules. A pterygoid process (,ptp) of the pterygo-quadrate bar is formed. The basihyal (bh) supports two broad ceratohyals (eh). The first two pairs of hypobranchials (hb 1-2) are noticed. A small independent cartilaginous second basibranchial (bb-2) is formed. It supports the third and fourth branchial arches.

STAGE 8: TOTAL LENGTH--6"0 MM (129 HR) (figmes 14 to 16) The ethmoid plate (ep) has further increased in size and it is broad in the middle. The parachordals (pc) form the basal plate (bp). Each orbital cartilage (orO extends behind to join the auditory capsule (ac). The side wall of the capsule (rac) is slightly better formed. The original large basicapsular fenestra (bcf) is invaded by cartilage and is restricted to about 80 microns in length. The basivestibular commissure (bvc) is complete. The metotic foramen (free), is formed which serves for the exit of IX and X cranial nerves. Meckel's cartilages (mc) fuse anteriorly to form a symphysis (mcu). Meckel's cartilage articulates with the pterygoquadrate cartilage. The basihyal and the first and second basibranchials have fused to form a common copula (cop). The first four branchial arches are represented by paired hypobranchials (hb 1-4) and ceratobranchials (cb 1-4). The first two epibranchials are noticed in the form of procartilages.

STAGE 9: TOTAL LENGTH--6"8 MM (195 HR) (figures 17 to I9) Anteriorly the ethmoid plate (ep) shows a distinct notch. The trabecula communis (tcom) is thin and plate-like. Lamina orbitonasales (lon) develop as small upgrowths from the postero-lateral sides of the ethmoid plate. Epiphysial cartilage (epb) is being formed. Its middle part is still procartilaginous. The floor of the auditory capsule (ac) is thickened. Meckel's cartilages (mc) posteriorly show a small retroarticular process (ra). The pterygoid process (ptp) has increased in size and is attached anteriorly to the ethmoid plate by connective tissue. The hypohyals (hh) are differentiated from the ceratohyals (ch). The common copula noticed in the previous stage breaks up into two copulae. The first copula (cop-l) supports the hypohyals (hh) and the first three pairs of hypobranchials (hb 1-3). The second copula (cop -2) supports the third and fourth pair of hypobranchials (hb 3-4) and the fifth branchial arch (ha-5). The first four epi- branchia.Is (ep 1-4) have appeared as small rod-like cartilages, which are connected with their respective ceratobranchials. The first two pairs of pharyngobranchials (pb 1-2) have appeared as tiny cartilages. 356 R.G. PASHINE AND V. B. MARATHE

Lon ep h. 'tcom roc .j--i~-c/i",, ptp

tc •

~ oa " eb-s

° .

cv -'-" cbp-I

Fig~es 17-19. 17. Dorsal view of the chondrocranium of C. carpio, stage 9 (6-8 ram). 18. Ventral view of the chondrocranium of stage 9, showing visceral arches. 19. Latelal view of the chondrocranium of stage 9. (E×pMnations for theabbreviations in figures are given in p. 363 )

STAGE 10: TOTAL LENGTH--8"6 ~ (285 HR) This is a slightly advanced stage than the previous one and the following changes are noted. The epiphysial cartilage is complete. Posteriorly the trabeculae become thin and are separated from the parachordals, and the hypophysial fenestra becomes obliterated. The roof of the auditory capsule is chondrified and a thin tectum synoticum is noticed in the posterior part of the chondrocranium.

STAGE 11: TOTAL LENGTH--10"5 MM (388 HR) (figures 20 and 21) The anterior mid-dorsal part of the ethmoid plate is elevated to form the nasal septum (ns). Sphenoseptal commissures (sphc) of the orbital cartilages unite with the nasal septum. The lamina orbitonasalis (lon) is well CHONDROCRANIUM OF Cyprinus carpio LINN. 357 ton

ab,.

~a Ot2~ :~ -~" ossified

Figures 20-21. 20. Dorsal view of the chondrocranium of C. ear~io, stage 11 (10"5 mm). 21. Ventral view of the chondrocranium of stage 11 (10"5 ram). (Explanations for the abbreviations in figures are givan in p. 363) developed and joins dorsally the o~bital cartilage. The trabeculae (tc~ extend behind for a short distance. The auditory capsule (ac) is well chondri- fled and shows all the three semicircular septa. Ventro-laterally it shows two depressions (hyf) for accommodating the hyosymplectic. A short, median dorsal extension from the roof of each auditory capusle is noticed. The tectum synoticum (tsy) is well represented. It extends behind for over 200 microns to form a conical process. The lateral commissure is partly replaced by bone. The anterior basicapsular commissure (abe) measures about 80 microns in thickness. The basicapsular fenestra (bcf) still persists. The basivestibular commissule (bvc) is vmy broad. The notochord (n) is noticed only in the posterior part of the basal plate. The posterio-median part of the basal plate shows a small ossified mea. The occipital arches (oa) are curved plate-like structures, supporting the hind brain. The visceral arches are well chondrified and have increased in size. The hyosymplectic cartilage shows two distinct knob-like structures, which fit into the two depressions of the auditory capsule (hyf). The second copula 358 R.G. PASHINE AND V. B. MARATHE seen in the previous stage, breaaks up into two basibranchials, namely, second and third. The second basibranchial supports the third pair of hypobranchials and the fourth pair of hypo-ceratobranchials. The third basibranchial is small and it supports the fourth hypo-ceratobranchials and fifth pair of ceratobranchials. All the four pairs of epibranchials and three pairs of pharyngobranchials have chondrified.

4. DISCUSSION

In many teleosts the trabeculae behind the ethmoid plate, fuse medially to form a trabecula communis but posteriorly they are free and continuous with the parachordals, enclosing a hypophysial fenestra. This type of cranium is called as tropitrabic cranium and it generally possesses an inter-orbital septum as in Syngnathus, 3 Clupea, 4 Anguilla, 5 Salmo, 1 Eleutheronema, n Trichopodus v and Mastacembelus. s In fishes like Gasterosteus, 9 Amiurus, 1° Silonia, Pangassius and Ailia ~1 and Labeo, ~2 the cranium is of the platytrabic type where the trabeculae remain apart and the inter-o~ bital septum is absent. In Cyprinus carpio, the hypophysial fenestra is noticed in a 4.4 mm embryo and the trabecula communis is formed in a 5.4 mm larva. The chondrocranium belongs to the tropitrabic type. Though the inter-orbital septum is not noticed in the chondrocranium, it is present in the adult fish. The manner in which the orbital cartilages appear is not uniform in the teleosts. In Gasterosteus, 9 Cyclopterus, 13 Triehopodus 7 and Tylosurus 14 the orbital cartilages develop in association with the epiphysial bar and in later stages they grow and join the laminae o~bitonasales anteriorly and the auditory capsules posteriorly. The orbital cartilage or taenia marginalis extends in front to form a sphenoseptal commissure, joining the nasal septum as noticed in Gasterosteus, 9 Salmo, 1 Gambusia, as Eleutheronema, 6 Trichopodus, 7 Tylosurus ~4 and Labeo? 2 In Mastacembelus, s in a 8.0 mm larva, a posterior orbital cartilage is noticed as an anterior prolongation of the auditory capsule. In a 9.7 mm larva an anterior orbital cartilage is well developed. It divides anteriorly into a small, median sphenoseptal commissure, fusing with the internasal septum and a small lateral spheneth- moid commissure, fusing with the lamina orbitonasalis. The anterior and the posterior orbital cartilages remain separate. The epiphysial cartilage is free and is not connected with any of the orbital cartilages. In Cyprinus, the orbital cartilages develop as slender, independent rods in a 5.4 mm larva and later join the auditory capsules in a 6.0 mm larva. In a 6.8 mm larva the outer parts of the epiphysial cartilage have chondrified in association with the orbital cartilages. The middle part is procartilaginous. In a 8.6 mm larva the epiphysial cartilage is complete and in later stages it remains connected with orbital cartilages. In a 10.5 mm larva the orbital cartilages are CHONDROCRANIUM OF Cyprinus carpio LINN. 359

well developed and extend anteriorly to join the lamina orbitonasales. Antero-medially the orbital cartilages join the nasal septum as the sphenoseptal commissures.

In the chondrocranium, the parachordals are connected to the auditory capgules by four commissures, viz., the lateral commissure, the anterior basicapsular commissure, the basivcstibular commissure and the posterior basicapsular commissure. But all the four commissures arc not present in one fish. The lateral commissure in Salmo 1 is formed by the union of two processes, the post-palatine process arising from the antero-lateral side of the basal plate and the pro-otic process coming from the anterior side of the auditory capsule. In Trichopodus 7 the lateral commissure appears in a 4.0 mm larva and in a 6-0 mm la va it is ossified. In Tylosurus 14 the lateral commissure is developed in a 7.8 mm larva. In Mastacernbelus, s the lateral commissure is noticed in a 8.0 mm larva and it is ossified in a 12.6 mm stage to form the pro-otic bone. Such a lateral commissure is absent in Arniurus, TM Silonia, Pangassius and Ailia 1~ and Labeo. 1~ Due to the absence of the lateral commissure the tAgemino-facialis chamber is not formed. In Cyprinus, the lateral commissure appears in a 5-4 mm larva. The pro-otic and the post-palatine processes, which generally go to form the lateral commissure, could not be made out in this fish. The lateral commissure is ossified in a 10.5 mm larva. In teleosts the auditoiy capsule is always connected with the anterior paL't of the parachordal bythe anterior basicapsular commissure, situated behind the exit of the facial nerve. The anterior basicapsular commissure is followed by a basicapsular fenestra. In Trichopodus 7 the anterior basicapsular commissure is ossified and is no longer cartilaginous in a 6"0 mm larva. In Cyprinus, the anterior basicapsular commissure appears in a 4.4 mm larva in the form of procartilage. It is chondrified in a 4.52 mm larva. Another commissure called the posterior basicapsular commissure is found between the exits of the glossopharyngeal and the vagus and it is present in Amiurus, 1° Anguilla, 5 Salmo, ~ Eleutheronema 6 and Mastacembelus.a In these forms the exit of the vagus is through the jugular foramen and that of the glossopharyngeal is associated with basicapsular fenestra. A basicapsular fenestra is noticed between the anterior and the posterior basicapsular commissures. In Clupea, ~ Gasterosteus, 9 Gambusia, a50phicephalus, ~8 Trichopodus, 7 Tylosurus ~4 and Labeo, TM the glossophalyngeal and the vagus leave the cranium through a common aperture the metotic foramen, separated from the basicapsular fenestra by a basivestibular commissure. In Cyprinus, an incomplete basivestibular commissure is noticed in

B 13--May 77 360 R.G. PASI-IINE AND V. B. MARATaE a 5.4 mm larva and it is well represented in a 6.0 mm stage. The metotic foramen is noticed in a 6.0 mm stage and it serves for the exit of the IX and X cranial nerves. The roof of the auditory capsule extends medially over the hind end of the brain-cavity to form a tectum synoticum, which is present in a number of teleosts like Gasterosteus, 9 Cyclopterus, 13 Anguilla, 5 Salmo, 1 Gambusia, ra Eleutheronema, e Trichopodus, 7 Mastacembelus, 8 Tylosurus 14 and Labeo ~. The tectum synoticum extends posteriorly as a median conical process over the major part of the occipital region as noticed in Trichopodus ~ and Labeo. ~ In Cyprinus, a thin tectum synoticum is formed in the posterior part of the auditory capsules in a 8.6mm larva. In a 10.5 mm stage the tectum synoticum becomes broad and extends behind as a median conical process over the occipital region. The basihyal appears independently of the first basibanchial in Tylosurus a4 in a 5"9 mm larva. In a 6.5 mm larva it fuses with the first basibranchial to form a common copula. In Mastacembelus, s a single median elongated copula is noticed in a 7.3 mm larva. In a 8.0 mm larva, a small second copula is also noticed. Later in a 9.0 mm lalva, a small independent basihyal cartilage is developed in front of the copula. In a 9.7 mm larva the basihyal is well developed and is attached to the median copula. In Tricho- podus 7 the basihyal does not arise as an independent chondrification but appea*s to be continuous with the basibranchial forming a common copula. Even in the fully formed chondrocranium it is continuous with the basibranchial. In Ophicephalus le the basihyal is continuous with the fused basi- hranchials forming the common copula. In Cyprinus carpio, independent chondrifications are laid down for the basihyal and the first basibranchial in a 5.0 mm larva. They fuse with each other in a 6.0 mm lmva to form a common copula. However, this common copula again breaks up into two in a 6.8 mm larva.

6. CONCLUSIONS

A large number of stages were fixed for the study of the development of the chondrocranium of Cyprinus carpio Linn. and eleven of them have been investigated. (a) In stage 1 (3-73 mm) the trabeculae are noticed in the form of procartilages. The notochord is present. (b) In stage 2 (4.28 mm) the trabeculae are cartilaginous. The parachordals are noticed as procartilages. (e) In stage 3 (4.4 ram) the trabeculae anteriorly unite to form a thin ethmoid plate and posteriorly join the parachordals enclosing CHONDROCRANIUM OF Cyprinus carpio Linn. 361 the hypophysial fenestra. The capsular cartilages are laid down in the anterior part of the auditory sac. The occipital arches have appeared. Meckel's cartilage, quadrate and hyosymplectic cartilage, ceratohyal and the first two pairs of branchial arches are noticed.

(d) In stage 4 (4.52 mm) a thin anterior basicapsular commissure is noticed. The hyosymplectic articulates with the anterolateral side of the auditory capsule.

(e) In stage 5 (4.7 mm) the parachordals extend behind to join the occipital arch elements. The hyosymplectic cartilage extends below the quadrate cartilage. The third and fourth branchial arches have appeared. 03 In stage 6 (5.0 mm) the posterior part of the parachordal is broadened. The cartilaginous basihyal and the first basibranchial have appeared as two independent rods. A small cartilaginous stylohyal is appearing. The fifth branchial arch is well formed.

(g) In stage 7 (5-4 mm) the large ethmoid plate extends behind as the trabecula communis. A thin lateral commissure is noticed in front of the anterior basicapsular commissure. These two commissures enclose a trigemino-facialis chamber through which V and VII cranial nerves pass. Posteriorly a basivestibular cornmissule is being formed. The orbital cartilages have appeared as small, independent rod-like cartilages. A distinct pterygoid process has appeared. First two pairs of hypobranchials and a small second basibranchial have appeared. (h) In stage 8 (6-0 mm) the orbital cartilages extend behind to join the auditoly capsules. The basivestibular commissure is complete. A small metotic foramen is formed. Mockel's cartilages form a symphysis in front. The basihyal and the basibranchials form a common copula. All the four hypobranchials have appeared. (i) In stage 9 (6.8 mm) a pair of laminae orbitonasales have appeared. The epiphysial cartilage has appeared and it is procartilaginous in the middle. Meckel's cartilage posteriorly forms a small retroarticular process. The pterygoid process extends up to the ethmoid plate. The hypohyals are differentiated from the ceratohyals. The common copula breaks up into two copulae. All the four epibranchials have appeared as small rod-like cartilages. The first and second pharyngobranchials have appeared. 362 R. G. PASX~gNEAND V. B. MARA'I~IE (j) In stage 10 (8.6 mm) the trabeculae become posteriorly disconnected from the parachordals, The epiphysial cartilage is complete. A thin tectum synoticum is noticed. (k) In stage 11 (10.5 mm) the-ethmoid plate is elevated antero-dorsally to form a nasal septum. The sphenoseptal commissures join the nasal septum. A median dorsal extension from the roof of each auditory capsule is noticed. The tectum synoticum is complete and posteriorly extends as a conical process. The lateral commissure is replaced by bone.

ACKNOWLEDGEMENTS

The authors wish to express their thanks to Dr. A. Gopalakrishna, Institute of Science, Nagpur, for providing necessary facilities and taking keen interest in the progress of the work.

REFERENCES

1. De Beer, G. R., The Development of the Vertebrate Skull, Oxford (1937). 2. Wijhe van, J. W., Verb. Akad. Wet. Amst. 5 47 (1902). 3. Kindred, J. E., J, Morphol. 35 425 (1921). 4. Wells, F. R., Proc. Zool. Soe. Lond. p. 1213 (1922). 5. Norman, J. R., Phil. Trans. B214 369 (1926). 6. Marathe, V. B. and Bal, D. V., Zool. Soc. India 8 107 (1956). 7. Marathe, V. B. and Bal, D. V., Proc. Indian Acad. Sci. 1346 347 (1957) 8. Bhargava, It. H., J. MorphoL 102 401 (1958). 9. Swinnerton, H. H., J. Micr. Sci. 45 503 (1902). 10. K.indred, J. E., Illinois Biol. Monogr. 5 7 (1919). 11. Srinivasachar, It. R,, Proc. Natl. Inst. Sci. India 1322 335 (1956). 12. Marathe, V.B. and Pashine, R. G., d. Biol. Sei. 15 85 (1972). 13. Uhlmann, E., Jena. Z. Natur. 57 275 (1921). 14. Marathe, V. B. and Suterwala, S. K., d. Univ. Bombay 1131 61 (1963). 15. Ramaswami, L. S., J. Mysore Univ. B6 19 (1945). 16. Srinivasachar, H. R., J. Linn. Soe. Zool. 42 238 (1953). 17. Bhargava, I-L H., J. Morphol. 104 237 (1959). CHONDROCRANIUM OF Cyprinus carpio Linn. 363

ABBREVIATIONS abc anterior basicapsular commissure ac auditory capsule as auditory sac ba 1-5 branchial arches 1-5 bb 1-2 basibranchials 1-2 bey basicapsular fenestra bh basihyal bp basal plate bye basivestlbular commissure cb 1-5 ceratobranchials 1-5 ch ceratohyal cop common copula cop 1-2 copulac 1-2 eb 1-4 epibranchials 1-4 ep ethmoid plate epb epiphysial bar fme metotic foramen hb 1-4 hypobranchials 1-4 hf hypophysial fenestra hh hypohyals hs hyosymplectic cartilage hyf groove for the articulation of the hyosymplectic lcm lateral commissure lon lamina orbitonasalis mc MeckeFs cartilage mcu Symphysis of Meckel's cartilages n notochord; ns nasal septum oa occipital arch ore orbital cartilage pb 1-2 pharyngobranchials 1-2 pc parachordal cartilage ptp pterygoid process of pterygoquadrate cartilage qu quadrate ra retro-articular process of Meckel's cartilage rac roof of auditory capsule sh stylohyal sphc sphenoseptal commissure tc trabecula tcom trabecula communis tyc trigemino-facialis chamber tsy tectum synoticum. B 14--May 1977