THE OLFACTORY APPARATUS. 



187 



relations and homologies can be treated best in a separate chapter 

 dealing with the hemispheres (Chapter XVIII). 



The primary relations of the olfactory apparatus to the rest 

 of the nervous system is one of the most difficult problems before 

 us. It has appeared in previous chapters that all the parts of 

 the nerv^ous system concerned with the reception of stimuli affecting 

 the bodily welfare of the organism in its surroundings are mor- 

 phologically as well as physiologically related. The stimuh to 

 which the sense organs respond are physical vibrations of some 



Tr. hab. ped. Valvula 

 Tr. olf. habenularis Tectum 



Tr. olf 

 Tr. olf hypothal. med. 

 Tr. olf. hypothal.. lat 



L. inferior 



Fig. ioi. — A diagram of the olfactory conduction paths in the sturgeon. £, epi- 

 triatum. The tractus strio-thalamicus is not lettered. It is placed horizontally in 

 the center of the figure. 



form (changes of pressure, sound- vibrations, light- vibrations), 

 and all of the peripheral and central organs have probably been 

 developed out of the general cutaneous nerves and centers as 

 a common fundament. On the other hand, the gustatory system 

 of nerves and centers is almost inextricably bound up with the 

 general visceral. This condition is readily understood if it be 

 true (p. 164) that the taste buds first appeared in the entodermal 

 lining of the pharynx to which the general visceral fibers were 

 already distributed. 



The olfactory organ is closely related in function with the 

 gustatory. The stimuli affecting both are changes in the chemical 

 character of the substances present in the indifferent water by 



