476 THE RABBIT CHAr. 



the organ of hearing ; the posterior aperture is called the 

 fenestra rotunda. On the internal or cranial surface of the 

 periotic is a large depression (//) which lodges the flocculus 

 of the cerebellum (Fig. 131). 



The olfactory capsules are roofed in by two long and 

 narrow nasal bones * {nas), which meet together in the 

 middle line and unite by suture with the frontals posteriorly. 

 Their side walls are formed by the bones which bear the 

 teeth of the upper jaw — the premaxilte (/. max) and 

 maxillcB (max), and in the median line below is a single 

 long and slender bone, deeply grooved on its upper surface, 

 and formed by the fusion of the two vomers * (vo). The 

 two nasal chambers are separated from one another in the 

 middle line by a median vertical plate of cartilage, the nasal 

 septum (Fig. 125 n.s) embraced below by the vomer. This 

 cartilage together with the cribriform plate and a median 

 vertical plate of bone (etli) extending forwards from the 

 latter into the septum, constitutes the mesethmoid. Within 

 the nasal chambers certain scroll-like folds of the mucous 

 membrane (Fig. 125) are present in order to increase 

 the surface, and in these, cartilages are developed. The 

 cartilages become ossified, and the resulting turbinal bones 

 unite with certain of the bones enclosing the olfactory organs, 

 and are named accordingly. The ethmoid turbinals (Fig. 

 123, e.tb) or true olfactory scrolls are two complicated, 

 folded bones united to the cribriform plate of the ethmoid, 

 and are covered in the fresh condition by the olfactory 

 epithelium ; the maxillo-turbinals (mx. tb) are similar but 

 more complex bones in the antero-ventral part of the nasal 

 cavities; and the naso-tiirbinals [ii.tb) are thin, folded 

 bones, much less complex, and fused with the inferior 

 surface of the nasals. 



In the front wall of each orbit, fitting comparatively loosely 



