Chap. I.] THE NEKVOUS SYSTEM IN THE ZOOLOGICAL SEfilES. 878 



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

 spheres of the beavei-, 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 



Fio. 64. 



Differentiation of the anterior brain ; A, brain of tortoise ; B, brain of a foetas of ca^; C, 

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

 anterior biain ; and on the right the fonr-pillared fornix. In C has been removed on the 

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

 enough to permit the cnrvation toward the base of the Gomu Ammonis to be seen. In 

 all the figures i 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 ; Ti, large foot 

 of the hippocampus ; ar, 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 i^ to say 

 in the grand conscious nervous." centre. Most of the other 

 nervous branches have, at least a)pparently, their origin in the 

 spinal marrow. 



