CHAP. VIII.] 



AND OF AMPHIBIA. 



115 



smooth, convex, semi-ovoid, or tongue-like body (fig. 49, d). 

 According to Professor Owen, the cerebellum is " very small 

 in the lazy Lump-fish, and extremely large in the active 

 and warm-blooded Tunny." It attains its highest develop- 

 ment, however, in Sharks (fig. 48, c). In these most active 

 and predaceous fishes the cerebellum not only covers much 

 of the medulla, but advances forwards over the optic lobes, 

 and the extent of its surface is further increased by the 

 existence of numerous superficial folds or indentations. 

 In front of the cerebellum are two rounded ganglia known 



FIG. 49. 



FIG. 48. Brain of the Shark (Carchar ias), side view. (Owen.) p, Cerebral hemi- 

 sphere ; o, optic lobe ; o, cerebellum with surface folds (ra) ; R, olfactory ganglion, 

 giving off (1) olfactory nerves ; 2, junction of olfactory peduncle with cerebral lobe ; 

 x, Cms cerebri ; IP, pineal body ; n, hypoaria ; p, pituitary body ; 2, optic nerve ; 

 3, oculo-motor nerve ; 5, trigeminus ; 7, auditory ; 8, vagus. 



FIG. 49. Brain of Roach, a, Olfactory peduncles ; b, cerebral lobes ; c, optic lobes ; 

 d. cerebellum ; e, medulla ; /. optic nerves. (After Spurzheim.) 



as the Optic Lobes (fig. 49, c), which correspond with 

 the principal part of the Insect's brain. The optic nerves 

 are connected with their under surface ; and they decussate 

 (figs. 51, 57), so that the one proceeding from the right eye 

 passes to the left optic lobe, and that from the left eye to 

 the right optic lobe. This new kind of cross arrangement 

 will, in a later chapter, be referred to in detail, since, with 

 slight differences, it also exists in other Vertebrates, and, 

 moreover, seems gradually to extend to other parts of 

 the nervous system. 



I 2 



