THE SKULL. 227 



capsules, which are cartilaginous capsules investing the nose 

 and the ear respectively. These latter are at first independent 

 of the cranium, but 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 below. 



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 



Fig. 47. Scyllium 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-mandibular cartilage. H, cerato-hyal. |, 

 pharyngo-branchial. K, epi-branciiial. |_, cent to- branchial. M, extra-bran- 

 chial. N, vertebral neural plate. N.C, olfactory capsule. O. centrum of ver- 

 tebra, p, intervertebral mniral plate. R, neural spine. S foramen jor the 

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

 nerve. U orbital 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, foramen for fourth 

 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 glossopharyngeal nerve. 



