212 COMPARATIVE MORPHOLOGY OF VERTEBRATES 



Jacobson's organ (vomero-nasal organ) is laid down in the embryo 

 of most mammals as a groove or pocket on the lower medial side of 

 each nasal cavity, opening in rodents and in man near the duct of 

 Stenson's gland; in other mammals, so far as known, its duct becomes 

 cut off from the nasal cavity and opens into the naso-palatal canal. 

 Its medial wall is covered with sensory epithelium, supplied by a 

 branch of the olfactory nerve. In the primates the organ is more or 

 less degenerate in the adult. 



There are two kinds of glands in the nasal cavity, the smaller and scattered 

 Bowman's glands and the larger Stenson's gland lying in the lateral ventral 

 wall and opening into the vestibule. There are usually several sinuses in the 

 bones of the skull, connected with the nasal cavities by foramina. Chief of 



Fig. 227. — Lateral wall of nasal cavity of man, after Corning, eg, crista galli; 

 ci, cm, cs, inferior, middle and superior conchae; fpn, foramen palatinum ma jus; fsp 

 sphenopalatine foramen; ic, incisive canal; osm, opening of maxillary sinus; sf, frontal 

 smus; $s, sphenoidal sinus. 



these are the maxillary sinuses (antra of Highmore), the frontal and sphe- 

 noidal sinuses in the corresponding bones, the relations of which are shown in 

 fig. 227. Others may occur in other bones of the face. 



Mammals are characterized by an external fleshy nose, supported 

 by the nasal bones and by cartilages, developed in part from the eth- 

 moid cartilage of the embryo, in part from paired cartilages, a new 

 acquisition of the mammals. Beyond these skeletal parts is the 

 fleshy portion which may form a proboscis of considerable size (swine, 

 elephant shrew, elephant). 



