THE NERVOUS SYSTEM. 



617 



also the fillet, and send fibres to the occipital cortex of the brain. They 

 are closely associated with the median corpora" geniculata. 



Corpora Geniculata. These are two on either side, lateral or 

 outer and median or inner; the former is developed from the fore-brain, 

 the latter from the mid-brain. The lateral corpus geniculatum is at the 

 side of the crus and appears to be a swelling on the lateral division of 

 the optic tract. Similarly the median appears to be the termination of 

 the median division of the optic tract. They both contain gray matter 

 (fig. 363). 



Corpora Dentata are plicated areas of gray matter in the interior 

 j)f the cerebellum, not unlike the olivary body of the bulb. The fibres 

 from each pass chiefly to the superior peduncle of its own side. 



The Cerebrum. For convenience of description, the surface of 

 the brain has been divided intone lobes (Gratiolet). 



parieta-ocdp* 



Fli depass. 



asctampM. 



Fig. 370. Left hemisphere, from without. (After Eberstaller.) 



1. Frontal (fig. 370), limited behind by the fissure of Eolando 

 (central fissure), and beneath by the fissure of Sylvius. Its surface con- 

 sists of three main convolutions, which are approximately horizontal in 

 direction, and are broken up into numerous secondary gyri. They are 

 termed the superior, middle, and inferior frontal convolutions. In ad- 

 dition, the frontal lobe contains, at its posterior part, a convolution 

 which runs upward almost vertically (ascending frontal), and is bounded 

 in front by a fissure termed the praecentral, behind by that of Rolando. 



2 Parietal. This lobe is bounded in front by the fissure of 

 Rolando, behind by the external perpendicular fissure (parieto-occipital), 

 and below by the fissure of Sylvius. Behind the fissure of Rolando is 

 the ascending parietal convolution, which swells out at its upper end 

 into what is termed the superior parietal lobule. The superior parietal 

 lobule is separated from the inferior parietal lobule by the intra-parietal 



