Mammalia: Nervous System 



677 



who lives in the dusty and sooty air of a city has daily demonstration 

 of this. 



Each of the large paranasal sinuses of the forepart of the head — 

 the maxillary sinus (antrum of Highmore), the frontal sinus, 

 and the sphenoid sinus — opens into the adjacent region of the nasal 

 cavity (Fig. 507). In addition to these are several or many irregular 

 sinuses (the "ethmoid cells" of man) in the lateral ethmoid bones. 

 All of these sinuses are lined bv a continuation of the nasal mucous 



Fig. 507. Lateral wall of nasal cavity of man. 

 (eg) Crista galli; (ci, cm, cs) inferior, middle, and 

 superior conchae; (fpn) foramen palatinum majus; 

 (fsp) sphenopalatine foramen; (ic) incisive canal; 

 (osm) opening of maxillary sinus; (sf) frontal sinus; 

 (ss) sphenoid sinus. (After Corning. Courtesy, 

 Kingsley: "Comparative Anatomy of Verte- 

 brates," Philadelphia, The Blakiston Company.) 



epithelium, although, at least in man, it is thinner and less glandular 

 in the sinuses than elsewhere. In those mammals whose sense of smell 

 is especially keen, olfactory cells may be found to a limited extent in 

 the frontal or the sphenoid sinus. In dogs olfactory cells have been 

 found in the epithelium of the region of the frontal sinus adjacent to 

 its opening into the nasal cavity. 



The nasal labyrinth is most highly elaborated in rodents, ungu- 

 lates, carnivores, and "edentates." It is well developed in lemurs but 

 more or less reduced in other primates. In aquatic mammals the ol- 

 factory apparatus is reduced to an extent depending upon the degree 



