190 ANATOMY OF THE RABBIT 



sculptured structure, almost completely enclosed by the membrane 

 bones of the face. Its features may be studied either in the divided 

 skull, or in one from which the roof of the nasal and cranial cavities 

 has been removed. It consists of three main portions, namely, 

 the cribriform plate, the perpendicular plate, and the paired lateral 

 masses or ethmoidal labyrinths. 



The cribriform plate (lamina cribrosa) is exposed to the anterior 

 cranial fossa. It is somewhat heart-shaped, with its apex in contact 

 with the ethmoidal processes of the orbitosphenoids. Its lateral 

 portions are perforated by numerous foramina, giving passage in 

 the natural condition to the branches of the olfactory nerves. Its 

 median portion forms a low vertical ridge, the crista galli, continu- 

 ous in front with the perpendicular plate. 



The perpendicular plate (lamina perpendicularis) is the bony, 

 posterior portion of the nasal septum, and as such is exposed to the 

 nasal cavity. It is united with the cartilaginous nasal septum and 

 also with the presphenoid. It forms the terminal member of the 

 chain of bones lying in the basicranial axis. 



The ethmoidal labyrinth (labyrinthus ethmoidalis) occupies 

 for the most part the posterior portion of the nasal fossa, but the 

 nasoturbinal extends forward to its anterior end, and is attached 

 for the greater part of its length to the internal surface of the nasal 

 bone. It is broadest in its middle portion, where it projects into 

 the space left between the ethmoturbinal proper and the maxillo- 

 turbinal, and contains at this point a pouch-like cavity, termed the 

 marsupium nasale. The whole structure is comparable to one 

 of the folds of the ethmoturbinal proper; but it is frequently seen 

 to be divided into anterior and posterior parts by a thin vertical 

 line of cartilage, the anterior division being probably allied to the 

 maxilloturbinal. Its middle, ventral portion bears a stout, back- 

 wardly-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 scrolls or 

 spaces contained by them. They are roughly comparable to the 



