416 THE NERVOUS SYSTEM. 



The Anterior Central Convolution runs outward and forward from 

 the great longitudinal fissure, along the front edge of the fissure of 

 Rolando. It is usually a single convolution, but is more or less folded 

 by transverse indentations. It communicates with the first frontal 

 convolution above and with the third frontal convolution below. It 

 also curves round the lower end of the fissure of Rolando, to unite 

 with the following convolution, which may be considered as its con- 

 tinuation. 



The Posterior Central Convolution is also parallel with the fissure 

 of Rolando, but behind it. Above, it turns backward, uniting with 

 the convolutions of the upper part of the parietal lobe. 



The Supra-marginal Convolution starts from the lower part of the 

 posterior central convolution and arches round the upper end of the 

 fissure of Sylvius. It then continues its curvilinear course, running 

 downward and forward, parallel with the inferior margin of the fissure 

 of Sylvius, toward the end of the temporal lobe. In this situation it 

 is known as the First Temporal Convolution. It is usually divided 

 throughout into two parallel convolutions by a secondary fissure run- 

 ning along its axis, and both these secondary convolutions are more or 

 less transversely folded. 



The Angular Convolution originates from the preceding and follows 

 the inferior edge of the parietal fissure to its posterior extremity, where 

 it makes a rather sharp turn downward and forward, whence its name 

 of the "angular convolution." It then becomes continuous with the 

 Second Temporal Convolution running downward and forward in the 

 temporal lobe. Below this convolution, and parallel with it, is the 

 Third Temporal Convolution, forming the inferior border of the 

 temporal lobe. 



In a horizontal section of the brain (Fig. Ill), the convolutions 

 are seen to penetrate its substance for varying distances at different 

 regions. In the anterior and posterior parts they leave a comparatively 

 thick layer of white substance between the cerebral ganglia and the 

 gray matter of the cortex. But on the side of the brain, at the situ- 

 ation of the fissure of Sylvius, the convolutions reach to a greater 

 depth. The cerebral ganglia are placed on each side the median line, 

 near the base of the brain ; the anterior pair, or the corpora striata, 

 being separated from each other in front by the anterior horns of the 

 lateral ventricles and the septum lucidum, and the posterior pair, or the 

 optic thalami, being separated in a similar manner by the third ventri- 

 cle except where they are united by the soft commissure and by the 

 peduncles of the pineal body and the posterior commissure. 



The corpora striata are penetrated from within and below by fibres, 

 which run to a great extent in distinct bundles, thus producing a visible 

 white striation in their gray substance. They form on each side, at 

 their anterior and lowermost part, a continuous mass ; but through- 

 out their remainder they are divided by a narrow band of white sub- 

 stance into two portions, namely, the caudate nucleus (6), so called 



