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 ofjadory capsules (o/f.) — thin rounded cartihiginous 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 font andlc : 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 orhit — over which 



P^th^^'^P^gph. 



Iri 



F]( 



bhy 



i. S13.— Hemiscyllium, lateral view of skull with visceral arches and anterior part of siainal 



column; the l)rancliial rays arc not reiiresented. The skull and hyoid arch arc somewhat 

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

 relations. 6r. i — ?/i'.5 branchial arches; ccr.hy. ceratohyal ; ip.br. epibranchials ; ((/.aperture 

 for glossopharyngeal nerve; li. Ity. basihyal ; hy. ma. hyoniandibular ; inttrc. intercalary 

 (interdorsal) jilates ; mrk. Meckel's c.:rtilage ; ncur. neural jirocesses ; olf. olfactoi'y capsule ; 

 oc. foramen for oculomotor; oj)t. optic foramen ; 7«(/. <j. palatoqu.adrate ; 7)(i(//. foramen for 

 4th nerve; ]ih. br.^ first pharyngobranchial ; jih. bi:=> fifth pharyngobranchial ; up. neural 

 si)iues ; tr. transverse processes and ribs ; tri. foramen for trigeminal nerve. 



is a ridge-like prominence, the sii2)raorhital crest, terminating 

 anteriorly and posteriorly in obscure processes termed respectively 

 the preorhital and postorlital jirocesses. Below the orbit is a 

 longitudinal infraorhital ridge. 



Behind the orbit is the cmclitm'y ree/ion of the skull — a mass of 

 cartilage in which the parts of the membranou.s labyrinth of the 

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

 portion of the skull are two small a])ertures situated in a mesial 

 depression. These are -the openings of the aqueductiis vestibuli 

 {endolymphatic duets)., leading into the vestibule of the membranous 

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

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



