THE CEREBRO-SPINAL NEKVOUS SYSTEM. 503 



continuation of the cerebro-spinal axis or column; on which, as a kind 

 of offset from the main nerve-path, the cerebellum is placed; and on the 

 further continuation of which in the direct line, is placed the cerebrum 

 (Fig. 343). 



When the two hemispheres are separated and turned to either side, a 

 broad connecting band or commissure, the corpus callosum, is seen. 



Convolutions of the Cerebrum. For convenience of description, 

 the surface of the brain has been divided intone lobes (Gratiolet). 



1. Frontal (F. Figs. 343, 344), limited behind by the fissure of Eo- 

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

 consists 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 



FIG. 343. Plan in outline of the encephalon, as seen from the right side. %. The parts are 

 represented as separated from one another somewhat more than natural, so as to show their con- 

 nections. A, cerebrum; /, gr, h, its anterior, middle, and posterior lobes; e, fissure of Sylvius; B, 

 cerebellum; C, pons Varolii; D, medulla oblougata; a, peduncles of the cerebrum; 6, c, d, superior, 

 middle, and inferior peduncles of the cerebellum. (From Quain.) 



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

 which runs upwards almost vertically (" ascending frontal"), and is 

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

 Eolando. 



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

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

 and below by the fissure of Sylvius. Behind the fissure of Eolando 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 

 sulcus. The inferior parietal lobule (pli conrbe) is situated at the pos- 

 terior and upper end of the fissure of Sylvius; it consists of (a) an ante- 

 rior part (supra-marginal convolution) which hooks round the end of 



