152 Anatomy of the Rabbit. 



It represents the similarly-named structure of the human skull, the 

 lowermost of three scroll-like bones, of which the remaining two, 

 the superior and middle turbinated bones, belong to the ethmo- 

 turbinal. In the natural condition it is covered by a non-olfactory 

 epithelium, and is thus distinguishable in function as well as in 

 position from the latter. 



12. THE MAXILLA. 



The maxilla, the largest element of the facial region, is asso- 

 ciated with its fellow of the opposite side to form the main portion 

 of the upper jaw. It consists of a central portion, the body 

 (corpus maxillae) , and of five processes, namely, alveolar, palatine, 

 orbital, zygomatic, and sphenoorbital. In the adult condition 

 the zygomatic bone is fused with the maxilla, so that the extent of 

 the zygomatic process appears to be greatly increased. 



The body of the maxilla is greatly fenestrated on its external 

 surface, the perforated area extending backward to the anterior 

 rim of the orbit, and thus including the maxillary fossa and the 

 infraorbital foramen. The dorsal boundary of the bone is 

 formed by the frontal process of the premaxilla and by the maxillary 

 process of the frontal. Anteriorly, it is united with the premaxilla, 

 the ventral part of the suture appearing in the diastema separating 

 the incisors from the cheek-teeth. The ventral portion of the bone 

 forms part of the lateral boundary of the incisive foramen. 

 Behind the palatine bridge it is applied to the lateral surface of the 

 palatine bone, and is projected into the orbit as a broad ridge en- 

 closing the alveoli of the four posterior cheek-teeth. 



In the divided skull the medial surface of the body of the maxilla 

 is found to be concealed by the ethmoturbinal. It contains a deep 

 longitudinal excavation, the maxillary sinus (sinus maxillaris), 

 widely open to the nasal fossa, but only seen to advantage when the 

 ethmoturbinal is removed. The lateral wall of che sinus corres- 

 ponds in position to the fenestrated area of the external surface. 

 It bears the chief part of the nasolacrimal canal. 



The alveolar process (processus alveolaris) is that portion of 

 the maxilla lodging the sockets of the cheek-teeth. In the rabbit 



