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NERVOUS SYSTEM. 



FIG. 224. Diagram of the human brain in a transverse vertical section 

 (Dalton). 



1, pons Varolii ; 2, 2, erura cerebri ; 3, 3, internal capsule ; 4, 4, corona 

 radiata ; 5, optic thalamus ; 6, lenticular nucleus ; 7, corpus cal- 

 losum. 



The directions of the fibres of the internal capsule are in general terms the 

 following : Fibres from the crura cerebri go directly into the corpora striata 



in front and into the 

 optic thalami behind. 

 This is the course of 

 greater part of. 

 fibres, but some 



the 

 the 



fibres go directly 

 through the internal 

 capsule, and thence 

 to the gray matter of 

 the cerebral convolu- 

 tions. Most of the 

 fibres, however, which 

 form the internal cap- 

 sule, come from the 

 gray matter of the 

 corpora striata and 

 optic thalami and 

 curve outward and 

 upward to go to the 

 gray matter of the 

 hemispheres. As they 

 pass from the internal capsule to the internal surface of the cerebral convo- 

 lutions, they form the corona radiata. 



In the human subject, lesions affecting the anterior two-thirds of the pos- 

 terior division of the internal capsule produce paralysis of motion only, and 

 are followed by descending degenerations. The fibres in this part are con- 

 nected with the corpora striata. Lesions affecting both the anterior two- 

 thirds and the posterior third of the posterior division of the internal capsule 

 produce paralysis of motion and sensation. The fibres in the posterior third 

 are connected with the optic thalami. Ascending degenerations have not 

 been observed in the fibres of the cerebrum. 



Tubercula Quadrigemina. These little bodies, sometimes called the 

 optic lobes, are rounded eminences, two upon either side, situated just below 

 the third ventricle. The anterior, called the nates, are the larger. These 

 are oblong, and of a grayish color externally. The posterior, called the testes, 

 are situated just behind the anterior. They are rounded and are rather 

 lighter in color than the anterior. Both contain gray nervous matter in 

 their interior. They are the main points of apparent origin of the optic 

 nerves and are connected by commissural fibres with the optic thalami. In 

 birds the tubercles are two in number, instead of four, and are called tuber - 

 cula bigemina. The anatomical and physiological relations of these bodies 

 will be fully described in connection with the sense of sight. 



Crura Cerebri. The crura are short, thick, rounded bands which pass 

 from the cerebral hemispheres to the upper border of the pons Varolii, 



