CHAP, i.] THE NERVOUS SYSTEM IN THE ZOOLOGICAL SERIES. 373 



in man. But here there are exceptions, and the cerebral hemi- 

 spheres of the beaver, like those of all the rodentia, for instance, 

 are almost smooth, while in the sheep exists a somewhat complex 

 system of circumvolutions. 



We have seen that in the arthropods the cerebroidal ganglion 

 has the privilege of furnishing always the optical nerves, and 



FIG. 64. 



Differentiation of the anterior brain ; A, brain of tortoise B, brain of a foetus of calf; C, 

 brain of a cat. In A and in B has been removed on the left the roof of the cavity of the 

 anterior brain ; and on the right the four-pillared fornix. In C has been removed on the 

 right side all the lateral and posterior portion of the anterior brain, and on the left 

 enough to permit the curvation toward the base of the Cornu Amrnonis to be seen. In 

 all the figures 1 represents the anterior brain ; II, the intermediary ; III, the median ; 

 IV, the cerebellum ; V, the spinal cord ; ol, the olfactory bulb (its communication with 

 the cerebral cavity figured in A) ; st, striated body; /, four -pillared fornix ; h, large foot 

 of the hippocampus ; sr, rhomboidal sinus ; g, geniculated protuberance. 



sometimes other nerves of the special senses. In like fashion, 

 in the vertebrates, the olfactory, optical, auditive, gustatory 

 nerves, in short all the nerves of the special senses, have their 

 original centre in the encephalon (optical layers), that is to say 

 in the grand conscious nervous centre. Most of the other 

 nervous branches have, at least apparently, their origin in the 

 spinal marrow. 



