14 



ANATOMY OF VERTEBRATES. 



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 f 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. Gyrencepliala. — In this subclass the prosencephalon 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 ( fornix ' is now maintained, not 

 only by the ' 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- 

 cepliala the exposed surface of the cerebral hemi- 



Bniiu of Cat, Felis domestica. ■. -i .1 ..-i r> i • i 



spheres may be smooth, or with tew and simple 

 fissures (fig. 96, Hyrax ; fig. 101, Tragulus ; and vol. ii. fig. 147). 

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



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 Assuring, may be 

 termed the ( oblique,' ' lon- 

 gitudinal,' and ' trans- 

 verse,' are presented by the 

 Gyrencepliala, and are ex- 

 emplified, respectively, in 

 the ungulate, unguiculate, 

 and quadrumanous divi- 

 sions of the subclass. Not- 

 withstanding, in these gene- 

 ral variations homologous 



pi. v., B g . 2(1836). 



Brain ol' (dralte. xcvir, 



