ANATOMY OF THE OLFACTORY ORGAN 



31 



and the less distinct proximal zone of basal nuclei. Each 

 of the olfactory nuclei is lodged in an oval cell-body. 

 Proximally this tapers rapidly into a fine olfactory nerve- 

 fiber wliich eventually enters the olfactory bulb of the 

 brain. Distally the body of the cell extends as a somewhat 

 coarser rod-like structure to the outer surface of the olfac- 

 tory epithelium where it ter- 

 minates in a small enlargement. 

 This enlargement has been 

 called the olfactory vesicle by 

 Van der Stricht (1909) who 

 ascribed to it a centrosomal 

 origin and believed it to play 

 a significant part in olfactory 

 reception. The olfactory vesi- 

 cle carries a cluster of proto- 

 plasmic filaments, the olfactory 

 hairs. (Fig. 7). These hairs 

 are apparently extremely deli- 

 cate and are easily destroyed; 

 hence they have escaped obser- 

 vation by many workers. They were probably seen in the 

 frog as early as 1855 by Eckhard, but they were first gen- 

 erally identified and thoroughly studied by Schultze (1856, 

 1862) in a number of vertebrates. Apparently they are 

 never very numerous; Schultze (1862) found that in the 

 frog there were five to six hairs on each olfactory cell 

 (Fig. 8), and von Brunn (1892) and Kalhus (1905) re- 

 corded six to eight in man. Eetzius (1894) noted two to 

 five hairs on each cell in the snake Tropidonotus. Ballo- 

 witz (1904) found ten to twelve or more in Petromyzon, 

 and Alcock (1910) states that in the pig the number varies 



Fig. 7. — Isolated olfactory cells 

 and sustentacular cells from man. 

 After von Brunn, 1892, Plate 30, 

 Fig. 4. 



