THE BONES OF THE SKULL 191 



superior and middle turbinated bones of the human skull, but in 

 the rabbit, as in most mammals, the ethmoturbinal surfaces are 

 relatively much more extensive than in man. 



In the typical mammalian skull the ethmoid bone is exposed 

 to the orbit, where it forms a thin plate of bone, the lamina papy- 

 racea. In the rabbit, however, the space usually occupied by the 

 lamina papyracea is partly filled by the lacrimal bone, the eth- 

 moidal process of the orbitosphenoid, and the sphenoorbital process 

 of the maxilla. 



The Inferior Turbinated Bone 



The inferior turbinated bone (concha nasalis inferior), or 

 maxilloturbinal, is a finely ridged structure, situated anteriorly in 

 the nasal fossa, and supported by the maxilla and premaxilla. 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. 



The Maxilla 



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

 ated 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 zygo- 

 matic 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 



