The Bones of the Skull. 151 



nasal cavity. It is united witii 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, 

 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 scrolls 

 ■or spaces contained by them. They are roughly comparable to the 

 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 

 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 orbitosphenoid and the sphenoorbital 

 process of the maxilla. 



11. 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. 



