OLFACTORY ORGAN. 



177 



Their lining of mucous membrane is in direct connection with that of the 

 nasal cavity ; this is also the case with the glandular organs of the nose, which 

 are divided into two sets, numerous small diffuse Bowman's glands, and a 

 large gland of Stenson. The early appearance of the latter in the embryo 

 indicates that it is an ancient structure (comp. nasal glands of Amphibia, Reptiles 

 and Birds, pp. 173-175). It lies inthelateral walls of the nasal cavity (Carnivora 



FIG. 147. TRANSVERSE VERTICAL SECTION THROUGH THE NASAL CAVITY OF 



MAN. 



/, II, III, inferior, middle, and superior turbinal ; a, b, c, inferior, middle, and 



cavity ; M, maxilla ; Or, Avail of orbit. 



Rodentia, &c), and in cases where a maxillary sinus is well developed (e.g. Man), 

 it extends into the latter, and lies in its inner wall, close to the aperture into 

 the nasal cavity. The duct opens at the anterior end of the middle turbinal. 



The appearance of an external nose is very characteristic of 

 the olfactory organ of Mammals ; we must regard it as a derivative 

 of the outer chamber of the nose of Reptiles and Birds. It is 

 formed by an extension outwards of the nasal bones, and by a 

 special cartilaginous support which arises from the ethmoid. The 

 outer nose undergoes the most varied functional adaptations ; it may 

 give rise to a trunk-like organ, or even grow out to form a definite 

 trunk, and, by means of its abundant nerve-supply, serve as a 

 delicate organ of touch, and even as a prehensile apparatus. It 

 is always provided with muscles, which are sometimes very largely 

 developed. 



JACOBSON'S ORGAN. 



By Jacobson's organ is understood a paired accessory nasal 

 cavity, which in an early embryonic stage becomes entirely separated 

 off from the nasal chamber, and which is supplied by the olfactory 

 and trigeminal nerves; it communicates with the mouth by a 

 special aperture. 5 



N 



