The: Bones of the Skull. 93 



stout, backwardly-directed uncinate process (processus uncinatus), 

 which is applied to the medial surface of the maxilla. 



The ethmoturbinal proper consists, as described above, of several 

 shorter scrolls, decreasing in length from above downward. Like the 

 posterior part of the nasoturbinal, they are attached, directly to the 

 cribriform plate, the perforations of which may be seen in the divided 

 skull opening into the ethmoidal cells (cellulae ethmoidales) or spaces 

 contained bv them. Thev are roughly comparable to the superior and 

 middle turbinated bones of the human skull, but in the rabbit, as m 

 most mammals, the ethmoturbinal surfaces are relatively much more 

 extensive than in man. 



In the tvpical mammalian skull the ethmoid bone is exposed to the 

 orbit, where it forms a thin plate of bone, the lamina papyracea. In the 

 rabbit, however, the space usually occupied by the lamina papyracea 

 is partly filled by the lacrimal bone, the ethmoidal process of the orbito- 

 sphenoid and the sphenoorbital process of the maxilla. 



11. THE INFERIOR TURBINATED BONE. 

 The inferior turbinated bone (concha nasalis inferior), or maxillo- 

 turbinal, is a finelv ridged structure, situated anteriorly in the nasal fossa, 

 and supported bv the maxilla and premaxilla. It represents the simi- 

 larly-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 ethmoturbinal. In the natural con- 

 dition it is covered by a non-olfactory epithelium, and is thus distinguish- 

 able in function as well as in position from the latter. 



12. THE MAXILLA. 



The maxilla, the largest element of the facial region, is associated 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, namelv, alveolar, palatine, orbital, zygomatic, and spheno- 

 orbital. 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 sur- 

 face, the perforated area extending backward to the anterior rim of the 

 orbit, and thus including the maxillary fossa and the infraorbital foramen. 

 The dorsal boundarv of the bone is formed by the frontal process of the 

 premaxilla and bv the maxillarv 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 enclosing the alveoli of the four posterior cheek-teeth. 



In the divided skull the medial surface of the bodv of the maxilla is 

 found to be concealed bv the ethmoturbinal. It contains a deep longitu- 



