[ANATOMY OF THE OLFACTORY ORGAN 



31 



Ak- 



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 which 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 Kallius (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 



Fio. 7. Isolated olfactory cells 

 and sustentacular cells from man. 

 After von Brunn, 1892, Plate 30, 

 Fig. 4. 



