214 



PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



group, the latter including the cetacea (whale, porpoise, dolphin). 

 The osmatic group, in turn, has been divided into the microsmatic 

 and macrosmatic animals, the latter class including those animals 

 in which the sense of smell is highly developed, such as the dog 

 and rabbit, while the former includes those animals, such as man, 

 in which this sense is relatively rudimentary.* The peripheral 

 end-organ of smell consists of the olfactory epithelium in the upper 

 portion of the nasal chambers. The physiology of this organ will 

 be considered in the section on Special Senses; The epithehal 



Fig. 96. — Diagram of olfactory paths: I, Olfactory bulb; //, olfactory tract; 777, olfac- 

 tory area on base of brain; 7 F, olfactory cortex (uncinate gyrus); F, anterior commissure; 

 .4, olfactory epithelial cells in nose; B, glomeruli in olfactory bulb; C, mitral nerve cells. The 

 fibers from the mitral cells end in nerve cells in the olfactory area, whence their path is con- 

 tinued by a third neuron to the cortex of the uncinate gyrus on the same side and po.'»sibly also 

 by fibers crossing in the anterior commissure to the hippocampal cortex on the other side. 



cells of which it consists are comparable to bipolar ganglion 

 cells. The processes or hairs that project into the nasal chamber 

 are acted upon by the olfactory stimuli, and the impulses thus 

 aroused are conveyed by the basal processes of the cells, the olfac- 

 tory fibers, through the cribriform plate of the ethmoid bone into 

 the olfactory bulb. 



The Olfactory Bulb and its Connections. — The olfactory bull s 

 are outgrowths from and portions of the cerebral hemispheres. 

 Each bulb is connected with the cerebral hemisphere by its ol- 



* See Barker, "The Nervous System," 1899, for references to literature. 



