468 THE INTERNAL STRUCTURE 



upon as special out-growths or prolongations from the 

 Brain. A distinction of this kind is undoubtedly legiti- 

 mate in regard to many of the lower animals. It is so, 

 for instance, in Fishes as well as in some Keptiles and 

 Mammals, in which the Olfactory Centres are extremely 

 well developed ; and also in Insects and Cephalopods in 

 which the eyes and Optic Centres are very large. But in 

 Man, in whom neither the sense of Smell nor the sense of 

 Sight is so inordinately developed, and in whom the cor- 

 responding primary Centres are relatively small, any such 

 distinction is less obvious. In his case, indeed, there is 

 no good reason for maintaining it, in regard to the Optic 

 * tracts,' since these parts differ little in appearance from 

 ordinary nerves. There is more reason, however, for such 

 a distinction in reference to the Olfactory ' tracts,' because 

 even in Man the Olfactory Ganglia exist as outlying por- 

 tions of the Brain, from which minute Olfactory Nerves 

 descend to the nasal passages. 



The course and central connections of these parts 

 require to be briefly set forth. 



The Olfactory ' tract ' is connected with the posterior 

 region of the orbital surface of the Hemisphere by three 

 roots ; of these the external goes outwards to the inferior 

 extremity of the Temporal Lobe of the same side, as 

 may be easily recognized in those Mammals in which the 

 Olfactory Lobes are large, though only with some difficulty 

 in Man. The inner root enters the Hemisphere near its 

 inner border, and a little in front of the Optic Com- 

 missure. The further relations of the fibres of the 

 Olfactory Tracts, and the fact that they come into relatioi 

 on each side with Convolutions of the corresponding am 

 not with those of the opposite Hemisphere will be subs* 

 quently referred to (see pp. 482, 488). 



The Optic ' tracts ' are the continuations of the Optic 



