178 ANATOMY OF THE RABBIT 



cuius, a small stalked appendage of the cerebellum. Ventral to 

 this fossa, and also somewhat in front of it, a thin ledge of bone 

 extends over an oval opening, the internal aperture of the facial 

 canal (canalis facialis), which serves for the transmission of the 

 seventh cranial (facial) nerve. Immediately behind and below this 

 aperture is the opening of the internal acoustic meatus (meatus 

 acusticus internus) for the transmission of the eighth cranial 

 (acoustic) nerve. The two apertures tend to be enclosed by a 

 shallow bony ridge, largely formed by the projecting ledge described 

 above, and resembling superficially the complete common tube 

 represented by the internal acoustic meatus of the human skull. 



In the bisected skull it is seen that the division of the nasal 

 cavity into right and left fossae is effected chiefly through a median 

 vertical, cartilaginous plate, the nasal septum (septum nasi), or 

 cartilaginous portion of the mesethmoid. This is continuous 

 posteriorly with a small crescentic vertical plate of bone, the 

 perpendicular plate (lamina perpendicularis) of the ethmoid bone 

 • — the bony portion of the mesethmoid^and the latter is also the 

 terminal element of the series of median bones constituting the 

 basicranium. Posteriorly, the ventral portion of the cartilaginous 

 nasal septum is supported by a vertical bony plate, the vomer, 

 the dorsal margin of which is grooved to receive it. Anteriorly, the 

 nasal septum bears on its ventral margin the paired enclosures of 

 the vomeronasal organ, which are also supported by the grooved 

 surface formed in the middle line by the adjacent dorsal surfaces 

 of the palatine processes of the premaxilla. The relations of these 

 structures, as well as of the cartilage supporting the nasopalatine 

 duct, are best seen in very young animals (cf. Plate III). 



The delicate, folded, or scroll-like turbinated bones, charac- 

 teristic of the nasal cavity, are borne on its posterior and lateral 

 walls. Occupying the anterior portion of the lateral wall of the 

 nasal fossa is a finely-ridged mass of bone, the concha inferior, or 

 maxilloturbinal. It is easily distinguishable from a more dorsal 

 and posterior series of broader folds, which together constitute 

 the ethmoturbinal. In the rabbit, as in mammals generally, the 

 latter is divisible into a more dorsal elongated portion attached 

 to the nasal bone, the nasoturbinal, and a more ventral and 

 posterior portion, the ethmoturbinal proper, composed of several 



