196 



O^ THE STRUCTURE OF THE SKULL. 



in that it lies above, and not below, the forward continuation of 

 the cranial cavity (Fig. 78). Usually, an inter-orbital septum is 

 formed by the compressed floor of the skull ; here it is constituted 

 by the compressed roof. Two chambers for the olfactory sacs 

 (N, Na) terminate the skull anteriorly and inferiorly ; and they, 

 the lips and the anterior part of the snout, are protected and 

 supported by a number of accessory cartilages (d to m). 



Below the auditory and orbital regions, and in front of the 

 latter as far as the nasal capsules, the base of the skull gives off 

 a broad cartilaginous sub-ocular plate (C, D, Fig. 78), the two 



Fig. 78. 



Fig. 78. — Vertical section of the skull of Chimoera monstrosa without the labial and nasal 

 cartilages. — A, the basi-occipital region ; P, the pituitary fossa ; Na, the partition 

 between the two olfactory sacs ; B, the alveolus for the anterior upper jaw tooth ; 

 I. Or., the inter-orbital septum ; asc, psc, anterior and posterior vertical semicircular 

 canals ; /., II. , V., VIII., exits of the olfactory, optic, fifth, and eighth pairs of 

 cerebral nerves. 



edges of which, sloping towards one another, bring it to a point at 

 n (Fig. 77 ; D, Fig. 78). With this part of the plate the mandible 

 (Mn) is articulated, while to the middle of its posterior margin 

 (D, G, Fig. 78) the hyoiclean apparatus (o, Fig. 77) is attached. 



A vertical section of the skull (Fig. 78) shows that the proper 

 cranial cavity consists of a large posterior chamber, divided by a 

 long and comparatively narrow neck from a much smaller, but 

 still large, anterior chamber. The latter contains the olfactory 

 lobes, and presents on each side, in front, a sort of cribriform 

 plate, through which the filaments of the olfactory nerve pass 



