THE HEMISPHERES. 475 



The Supra-Sylman or Supra-marginal Convolution (6) starts from the 

 lower end of the posterior central convolution and thence arches round 

 the extremity 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 anterior extremity of the temporal 

 lobe. In this situation it is known as the First Temporal Convolution (7). 

 Throughout its course, it is generally divided into two parallel convolu- 

 tions by a secondary fissure running along its axis, and both of these 

 secondary convolutions are more or less folded transversely. 



The Angular Convolution (8) originates from the preceding and follows 

 the inferior edge of the parietal fissure backward 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 (9) running downward and forward to 

 the extremity of the temporal lobe. Below this portion, and running 

 parallel with it, is the Third Temporal Convolution (10) which forms the 

 inferior border of the temporal lobe. 



The Upper Parietal Convolution (11) is situated above the parietal 

 fissure, between it and the posterior part of the great longitudinal 

 fissure. Like the corresponding frontal convolutions, it is much divided 

 by irregular secondary foldings, and is connected with other convolutions 

 which are concealed within the great longitudinal fissure. There are also 

 a number of Occipital Con volutions (12), both longitudinal and transverse, 

 but these are not conspicuous in a lateral view of the cerebral hemi- 

 spheres. They are more or less continuous with the upper parietal con- 

 volution above, and with the second and third temporal convolutions 

 below. 



On a transverse horizontal section of the brain, the convolutions are 

 seen to penetrate into its substance for varying distances at different 

 regions. In the anterior and posterior parts the foldings are more 

 nearly regular in depth, and leave a comparatively thick layer of white 

 substance between the cerebral ganglia and the gray matter of the con- 

 volutions. But at the sides of the brain, at the situation of the fissures 

 of S} T lvius, the convolutions reach to a much greater depth. The cere- 

 bral ganglia are placed on each side the median line, near the centre 

 of the brain; the corpora striata being separated from each other ante- 

 riorly by the septum lucidum and the cavity of the lateral ventricles, 

 and the two optic thalami being separated in a similar manner by the 

 cavity of the third ventricle, except where they are united by the- soft 

 commissure. 



The optic thalami (Fig. 157, 9 ) are surrounded on their outer borders, 

 and separated from the corpora striata, by a band of white substance, 

 the internal capsule ( 10 ) consisting of fibres passing upward from the 

 crura cerebri. The corpora striata (*, 8 ) form on each side, at their in- 

 ferior portions, a continuous mass of gray substance; but for the greater 

 part of their thickness they are divided into two parts by a tract of 

 white substance, continuous with the internal capsule, and, like it, con- 



