14 ANATOMY OF THE RAT 



maxillary, and palatine bones. The two long prepalatine 

 foramina lie in its floor, and it communicates by a foramen 

 with each orbito-temporal fossa. A perpendicular median 

 partition, the nasal septum, divides the nasal cavity into 

 two nasaZ fossae. The septum is partly cartilaginous. 



Each nasal fossa contains three very delicate, folded 

 turbinal bones, which probably correspond to the maxillo- 

 turbinal, nasoturbinal, and ethmoturbinal bones of other 

 mammals. The first of these is an elongated thin sheet of 

 bone attached ventrally to the inner surface of the pre- 

 maxillary bone. The second is a process of the nasal bone. 

 Its ventral edge turns outward and upward like the rolled 

 edge of a stiff piece of paper. The ethmoturbinal bone is 

 much more extensively convoluted than the other tur- 

 binals. The convolutions inclose spaces known as ethmoi- 

 dal cells, whose long axes are, in general, directed antero- 

 posteriorly. The ethmoturbinals are attached posteriorly 

 to the cribriform plate. Examination of a skull in which 

 the bone has been removed from the side of the nasal fossa 

 shows that in the posterior part of the fossa the turbinal 

 bones extend from the top to the bottom of the cavity and 

 posteriorly almost to the optic foramen. The convolutions 

 of the turbinal bones, together with the flesh covering them, 

 are sometimes called the nasal lahyrinth. In mammals the 

 folds supported by the turbinals warm the air and extract 

 foreign bodies from it. The epithelium covering the ethmo- 

 turbinals contains olfactory cells which are stimulated by 

 odorous substances in the air. 



Consult a text on comparative anatomy to determine the 

 variations among vertebrates in the bones of the nasal 

 cavity. Compare the nasal cavity of the rat with the same 

 part in the turtle, frog, dogfish, etc. Assisted by a text on 

 embryology outline the stages in the evolution of the nasal 

 cavity. 



