148 



ZOOLOGY 



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 oJ factor ij ai^jsulcs (olf.) — 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 fon/.ancUc : 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 C(.incavity — the oi-tjit — over which 



iri 





i-pJt-.irs 



hhi/ 



:;. S13.— Hemiscyllium, laturiil \iu\v ..f fekull ^^'it]l vi^cc'iMl arcliL.saud ant ci-iui- part of sjiin.i] 

 L-(jliiiiiri ; tliu Ijr.Liichial rays arc in.tt represented. Tlie skull and hyuid areh are somewhat 

 drawn downwards, so that tlie liyoid and tirst brancliial arch ai'e not exactly in theii' natural 

 relations, /ir.l — hr.^ bi'anehial arches ; C(.;, ktj. cer<itoliyal ; e/i, br. epibrauchials ; 'jl. al»ertnrc 

 for glossopharyngcil nerve; /' hij. Ijasihyal ; ky. uui. hyoniandibular ; ^nUrc. intercalary 

 (iiitei dorsal) plates; iiick. Meckel's c.rtilage ; nevf. neiu'al processes; olf. olfactory eal>sule ; 

 or. foramen for ocuLimotor ; oj>t. optic foianicn ; juU. 7. palatoquadrate ; path, foramen for 

 4th nerve; t>k. In'.'^ first pharyngobi-anchial ; j>h. hr.^ fifth pharyngobranchial ; ^p. neural 

 spnics ; /<. transverse processes and ribs ; //■(. foramen fur trigeminal nerve. 



is a ridge-like prominence, the suprao rhital crcd, terminating 

 anteriorly and posteriorly in obscure processes termed resjjectively 

 the preoi'hitat and ^^ostoi'ftiifa/ processes. Below the orbit is a 

 longitudinal infraorljiial ridge. 



Behind the orbit is the auditurij region of the skull — a ina.ss of 

 cartilage in which the parts of the membranous labyrinth of the 

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

 jKjrtion of the skull arc two small apertures situated in a mesial 

 depression. These are the openings of the aqueductus vestihdo 

 {cndolym.phedic ducts), leading into the vestibule of the membranous 

 labyrinth. Behind this again is the oeeijAiul rec/ioii, forming the 

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



