606 NERVOUS SYSTEM. 



sure. The temporo-sphenoidal lobe is situated below the fissure of Sylvius 

 and in front of the occipital lobe. 



While the convolutions are not exactly the same in all human brains, or 

 even in both sides of the brain, their arrangement and relations may be 

 described in a general way with sufficient accuracy to enable one to recognize 

 easily the most important physiological points in the descriptive anatomy of 

 the cerebral surface. The diagrammatic Figs. 221 and 222 give a general 

 view of the fissures and of the most important convolutions. 



The first frontal convolution is bounded internally by the great longi- 

 tudinal fissure and externally by a shallow fissure nearly parallel to the longi- 

 tudinal fissure. The second frontal convolution lies next the first frontal 

 convolution, and is bounded externally by two shallow fissures lying in front 

 of the fissure of Sylvius. The third frontal convolution curves around the 

 short branch of the fissure of Sylvius. On either side of the fissure of Ro- 

 lando, are the anterior central convolution and the posterior central convolu- 

 tion. Curving around the posterior extremity of the fissure of Sylvius, is 

 the supramarginal convolution, which is continuous with the first temporal 

 convolution, the latter lying behind and parallel with the fissure of Sylvius. 

 Internal to the posterior portion of the intraparietal sulcus is the angular 

 convolution, which is continuous with the second temporal convolution. At 

 the inferior border of the temporo-sphenoidal lobe, below the first and second 

 temporal convolutions, is the third temporal convolution. The superior pari- 

 etal convolution lies by the side of the median fissure and is the posterior 

 continuation of the first frontal convolution. The situation of the occipital 

 convolutions is indicated in Fig. 221. In addition to these convolutions 

 upon the general surface of the cerebrum, there are convolutions on the sur- 

 face of the base of the brain and in the gray matter of the sides of the great 

 longitudinal fissure. In the fissure of Sylvius, near its ascending branch, 

 between the anterior and the posterior lobes of the brain and beneath the 

 third frontal convolution, is a group of convolutions constituting the island 

 of Reil. 



Fig. 222 shows the most important parts observed on the inner surface 

 of the right hemisphere. These parts do not demand any explanation beyond 

 that given in the diagram itself. 



Basal Ganglia. The ganglia at the base of the brain are the olfactory 

 ganglia, the corpora striata, optic thalami, tubercula quadrigemina and the 

 gray matter of the pons varolii. The olfactory ganglia will be described in 

 connection with the physiology of the sense of smell. The corpora striata 

 and the optic thalami are important in their relations to the internal capsule 

 and the paths of motor and sensory conduction. 



Corpora Striata, Optic Thalami and Internal Capsule. The corpora 

 striata are pear-shaped bodies, situated at the base of the brain, with their 

 rounded bases directed forward, and the narrower ends, backward and out- 

 ward. Their external surface is gray, and they present, on section, alternate 

 striae of white and gray matter. Between the posterior and narrow extremi- 

 ties of these bodies, are the optic thalami. The corpora striata have what is 



