256 THE NERVOUS SYSTEM 



Nor can it be doubted that an animal thus mutilated feels 

 pain. It is probable that the sensory impression is received by 

 some of the gray centers in the pons itself, but not being con- 

 veyed to the cerebrum, is not remembered. 



The Crura Cerebri, Corpora Striata, Optic Thalami, Internal 

 Capsule and Corpora Quadrigemina. 



It will be well before discussing the cerebrum to consider 

 briefly other collections of gray and white matter in the neigh- 

 borhood of the upper part of the pons. 



The crura cerebri, passing upward from the anterior part of 

 the pons, diverge to run apparently underneath the corpora 

 striata and optic thalami in the direction of the cerebral hemis- 

 pheres. They are about j inch long and slightly broader above 

 than below. The main bulk of each crus consists of white fibers, 

 but a collection of gray matter (locus niger) divides the band into 

 a lower or superficial section, called the crusta, and an upper or 

 deep section, called the tegmentum. There is also some gray 

 matter in the tegmentum proper. The fibers of the tegmentum 

 are supposed to convey afferent impressions chiefly, and end for 

 the most part in the optic thalamus, though some are continued to 

 the cerebrum through the internal capsule. The fibers of the 

 crusta are supposed to convey efferent impulses, and pass to the 

 corpus striatum and the cerebrum. 



It is evident that the function of the crura is mainly to con- 

 duct messages to and from the parts above. It is said that the 

 locus niger is concerned in coordination of the movements of 

 the eye-ball and iris. 



The Corpora Striata, Optic Thalami and Internal Capsule 

 are closely related and are best considered together. 



Each corpus striatum is pear-shaped with its large end forward 

 and near the median line; the posterior small extremities are 

 divergent from each other and embrace the two optic thalami. 

 Externally they are white; internally white and gray elements 



