148 



ZOOLOGY 



SECT. 



of three cartilaginous rods converging as they extend forwards and 

 meeting at their anterior ends. At the sides of the base of this are 

 the olfactory capsules (off.) thin rounded cartilaginous sacs opening 

 widely below, the cavities of the two capsules being separated 

 from one another by a thin septum. The part of the roof of the 

 cranial cavity behind and between the olfactory capsules is formed, 

 not of cartilage, but of a tough fibrous membrane, and the space 

 thus filled in is termed the anterior fonfanelle : in contact with the 

 lower surface of the membrane is the pineal body, to be afterwards 

 mentioned in the account of the brain. Each side-wall of this 

 part of the skull presents a deep concavity the orbit over which 



netcr intcrc 



/1\ 



ffWff 



i7t.br. 3 



e.p.br.5 



FIG. 813. Hemiscyllium, lateral view of skull with visceral arches and anterior part of spinal 

 column ; the branchial rays are not represented. The skull and hyoid arch are somewhat 

 drawn downwards, so that the hyoid and first branchial arch are not exactly in their natural 

 relations, frr. 1 br. -5 branchial arches ; ccr. hy. ceratohyal ; tp. l>r. epibranchials ; ;/l. aperture 

 for glossopharyngeal nerve ; />. hy. basihyal ; hy. run. hyomandibular ; interc. intercalary 

 (interdorsal) plates; mck. Meckel's c; rtilage ; neur.- neural processes; olf. olfactory capsule ; 

 oc. foramen for oculomotor ; opt. optic foramen ; pal. q. .palatoquadrate ; path, foramen for 

 4th nerve ; ph. i>r. 1 first pharyngobranchial ; ph. br. 5 fifth pharyngobranchial ; up. neural 

 spines ; tr. transverse" processes and ribs ; tri. foramen for trigeminal nerve. 



is a ridge-like prominence, the supraorbital crest, terminating 

 anteriorly and posteriorly in obscure processes termed respectively 

 the precrbital and postorbital processes. Below the orbit is a 

 longitudinal infra-orbital ridge. 



Behind the orbit is the auditory region of the skull a mass of 

 cartilage in which the parts of the membranous labyrinth of the 

 internal ear are embedded. On the upper surface of this posterior 

 portion of the skull are two small apertures situated in a mgsial 

 depression. These are the openings of the aqueductHs vestibuli 

 (endolymphatic ducts), leading into the vestibule of the membranous 

 labyrinth. Behind this again is the occipital region, forming the 

 posterior boundary of the cranial cavity, and having in the middle 



