784 



SMELL 



[CH. LV. 



FIG. 483. Cells from the olfactory region of 

 the rabbit, st, Supporting cells ; r, r', 

 olfactorial cells ; /, ciliated cells ; s, cilia- 

 like processes; b, cells from Bowman's 

 glands. (Stohr.) 



contains numerous mucous glands. The olfactory region in man is 

 limited to a portion of the membrane covering the upper turbinal bone, 

 and the adjacent portion of the nasal septum ; it is only 245 square 

 millimetres in area. The cells of the epithelium here are of several 

 kinds : first, columnar cells not ciliated (fig. 483, st), with the broad 



end at the surface, and below 

 tapering into an irregular branched 

 process or processes, the termina- 

 tions of which pass into the next 

 layer: the second kind of cell (fig. 

 483, r) consists of a small cell body 

 with large spherical nucleus, situ- 

 ated between the ends of the first 

 kind of cell, and sending upwards 

 a process to the surface between 

 the cells of the first kind, and from 

 the other pole of the nucleus a pro- 

 cess towards the corium. The latter 

 process is very delicate, and may 

 be varicose. The upper process is 

 prolonged beyond the surface, where 

 it becomes stiff, and in some animals, such as the frog, is provided 

 with hairs. These cells, which are called olfactorial cells, are numerous, 

 and the nuclei of the cells not being on the same level, a compara- 

 tively thick nuclear layer is the result. They are in reality bipolar 

 nerve-cells. In the corium are a number of serous glands called 

 Bowman's glands. They open upon the surface by fine ducts passing 

 up between the epithelium cells. 



The distribution of the olfactory nerves which penetrate the 

 cribriform plate of the ethmoid bone and pass from this region to 

 the olfactory bulb is shown in fig. 484. The nerve-fibres are 

 the central axons of the bipolar nerve-cells we have termed olfac- 

 torial ; the columnar cells between these act as supports to them. 



The olfactory tract is an outgrowth of the brain, which is 

 originally hollow, and remains so in many animals ; in man the 

 cavity is obliterated, and the centre is occupied by neuroglia : 

 outside this the white fibres lie, and a thin superficial layer of 

 neuroglia covers these. The three "roots" of the olfactory tract 

 have been traced to the uncinate gyrus and hippocampal regions of 

 the same side of the brain, which is the portion experimentally found 

 to be associated with the reception of olfactory impulses (see 

 pp. 698 and 738). From the cells of the grey matter here fibres pass 

 by a complex path to the corresponding regions of the opposite 

 side. There is also a communication via the corpora mammillaria 

 with the optic thalamus and te^mentum of the mid-brain. 



