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 
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