THE SKULL. 219 



capsules, which are cartilaginous capsules investing the nose 

 and the ear respectively. These latter are at first independent 

 of the cranium, hut in the adult fuse with it, forming lateral 

 expansions of its anterior and posterior ends. This fusion of 

 the sense-capsules and cranium is so complete that they will 

 be described together. 



1. General form of the skull. 



The skull is a somewhat oblong box of cartilage, 

 deeply hollowed at the sides to form the orbits, 

 which lodge the eyes, and ending in front in a 

 short pointed rostrum formed by three converging 

 rods. 



The olfactory capsules are thin-walled lateral 

 expansions of the anterior end of the skull, in front 

 of the orbits ; and the auditory capsules are more 

 massive projections behind the orbits. 



Examine the several surfaces of the skull in succession, 

 identifying the parts described beloiu. 



2. The dorsal surface of the skull, 



a, The olfactory capsules are a pair of large oval 

 cartilaginous cups-at the anterior end of the skull : 

 they have very thin walls and are easily torn. 

 Their long axes are placed somewhat obliquely. 



Fig. 45. — Soyllium canicula. The skull and visceral skeleton with the 

 anterior part of the vertebral column, seen from the right side. 

 The labial cartilages and gill-rays are omitted, (a. m. m.) 



A, auditory capsule. B, post-orbital groove. C, inter-orbital canal. E, 

 upper jaw. F, lower jaw. G, liyo-maudibular cartilage. H, cerato-byal. I, 

 pharyngo-branchial. K, epi-brancbial. L, ceratj-brancliial. M, extra- 

 brauchial. IT, vertebral ueural plate. M"C, olfactory capsule. O, centrum 

 of vertebra. P, intervertebral ueural plate. R, neural spine. S, foramen for 

 the ventral root of a spinal uerve. T, foramen for the dorsal root of the 

 same nerve. U, ortrital grooves, lodging the ophthalmic branches of the fifth 

 and seventh nerves. . "W", aperture at end of orbital groove through which the 

 ophthalmic branches of the fifth and seventh nerves leave the orbit. ' Y, 

 foramen for hyoidean artery Z, ethmo-palatine ligament. 



II, optic foramen. Ill, foramen for third nerve. IV, foremen for 

 fourtli nerve. "V, foramen for the main branches of the fifth and seventh nerves, 

 and for the sixth nerve. Va, foramen for the ophthalmic branch of the fifth 

 nerve. Vila, foramen for the ophthalmic branch of the seventh nerve. IX, 

 foramen for the ninth or glosso-pharyngeal nerve. 



