114 



ANATOMY OF VERTEBRATES. 



83 



simplicity of folds on the exposed surface of the hemispheres in a 

 few, their absence in most; the connection of the two hemispheres 

 by a ( corpus callosum,' as well as by the ' lyra ' and ( anterior 

 commissure,' the absence of the ( septum lucidum,' and the pro- 

 portionally large hippocampi and bigeminal bodies. 



C. Gyrencephala.--Ln this subclass the proscncephalon is rela- 

 tively larger, extending backward more or less 

 over the cerebellum with a concomitantly de- 

 veloped ' corpus callosum,' the connection of 

 which with the f fornix ' is now maintained, not 

 only by the f lyra,' but by the attenuated ver- 

 tically extended subjacent parts of the medial 

 walls of the lateral ventricles called ' septum 

 lucidum,' their interspace being the ' fifth ven- 

 tricle' of Anthropotomy, fig. 118, n. 



In some of the smallest species of Gyren- 

 cephala the exposed surface of the cerebral hemi- 



Brain. of Cat, Fclis domestica. -i . -i . , P -, . -, 



spheres may be smooth, or with lew and simple 

 fissures (fig. 96, Hi/rax ; fig. 101, Tragulus ; and vol. ii. fig. 147). 

 This state does not, however, relate to reduction of heinispheres, 



F4 but may coexist with their 



extension over the whole 

 cerebellum, 1 as in some 

 small Quadrumana, fig. 

 109, Midas and Callithrix ; 

 but the increase of super- 

 ficial grey matter by fissures 

 and folds is now the rule. 



Three leading patterns of 

 convoluted surface, which, 

 from the prevalent direc- 

 tion of fissuring, may be 

 termed the ( oblique,' ' lon- 

 gitudinal,' and ' trans- 

 verse,' are presented by the 

 Gyrencephala, and are ex- 

 emplified, respectively, in 

 the ungulate. unguiculate. 



O O 



and quadrumanous divi- 

 sions of the subclass. Not- 

 withstanding, in these gene- 

 ral variations homologous 



" i.ir.-illu. 



1 LXX-. pi. v., fig. 2 (1836). 



