Ill 



ENDOSKELETON 



ENDOSKELETON OF HEPTANCHUS MACULATUS 



The endoskeleton in Hepianchus maculatus consists of a framework of rela- 

 tively simple cartilage which serves as a protection for the various internal 

 organs and at the same time acts as a support for the attachment of the mus- 

 culature of the body. The cartilage of the axial part, the skull and the spinal 

 column, is essentially like that of the appendages in that it has but little cal- 

 cium deposited in it. 



Axial Skeleton 



SKULL 



The skull of Heptanchus maculatus is composed of (1) a relatively thin-walled 

 cranium or brain case to which in the adult are fused the nasal and auditory 

 capsules, and (2) a series of cartilaginous visceral arches which support the 

 mouth and the pharyngeal region. 



The cranium in dorsal view (fig. 45) is like a violin box, broadly pointed in 

 front and almost square at the posterior margin. At the sides it is constricted, 

 and back of these constrictions are the heavy postorbital processes {po.p.) . In 

 the middorsal line at the posterior margin of the cranium is a ridge, the occipi- 

 tal crest {o.cr.) which lies posterior to a pit, the parietal fossa (p./.) ; from 

 the bottom of the fossa the foramina for the endolymphatic ducts {ed.) and 

 the fenestrae {fn.) lead to the ear. Inclosing the parietal fossa and pointed 

 backward is faintly indicated a V produced by the two anterior oblique semi- 

 circular canals. This V, together with a similar V produced by the posterior 

 oblique semicircular canals (see p.o.s.) and inclosing the occipital crest poste- 

 riorly, roughl}^ forms an hourglass. In front of the parietal fossa the roof is 

 slightly convex and extends to a large dorsally placed opening, the anterior 

 fontanelle (F.). 



On each side of the anterior fontanelle is a small foramen for the ophthal- 

 micus profundus nerve {f.o.p}), and at the sides of the posterior part of the 

 fontanelle are two (or one) large openings (f.o.VIP) for the ophthalmic 

 branch of the seventh cranial nerve. Running on a line posterior from this 

 large opening and parallel to the margins of the indenture is a row of smaller 

 foramina on each side, through which twigs of the same nerve pass. 



It will be observed that the cranium of Chlamydoselachus in dorsal view 

 (fig. 46) is much like that of Heptanchus. 



In side view (figs. 47 and 48) projecting forward there are the elongated 

 cartilaginous supports for the rostrum, at the sides of Avhich is the olfactory 

 capsule (ol.c) for the nasal apparatus. The cartilages of the capsules are 



[43] 



