THE BASAL GANGLIA 259 



cerebellum and contains one of the nuclei of origin of the optic 

 nerve. 



Regarding the function of the internal capsule it may be said 

 that its fibers are in main part prolongations from the crusta and 

 from the gray matter of the corpora striata; fibers also pass up- 

 ward through it from the tegmentum and the optic thalamus. As 

 a matter of fact, most of the fibers of the crura go directly into 

 the corpora striata (motor) and the optic thalami (sensory), but 

 some pass directly upward through the capsule. It is to be 

 noted, however, that the capsule does not consist of these last 

 named fibers alone, but of fibers from the corpora striata and 

 optic thalami as well. Observations show that pathological 

 lesions affecting the anterior two-thirds of the posterior division 

 of the internal capsule are followed by paralysis of motion; that 

 lesions affecting only the posterior one-third of the posterior di- 

 vision are followed by anesthesia; and that lesions affecting 

 the entire posterior limb are followed by both paralysis and an- 

 esthesia these phenomena always manifesting themselves on the 

 side opposite the lesion only. This leads to a definite conclusion ; 

 viz., that efferent fibers occupy the anterior two-thirds and afferent 

 fibers the posterior one-third of the posterior limb of the capsule. 



Nothing conclusive can be said about the function of the ex- 

 ternal capsule or of the claustrum. 



The Corpora Quadrigemina, two on each side, are promi- 

 nences on the dorsal surface of the pons and crura above the aque- 

 duct of Sylvius. They contain white and gray matter. The pos- 

 terior tubercle's are connected with the eighth nerve, the sen- 

 sory tract, the temporal region of the brain, and the lateral cor- 

 pora geniculata. The anterior tubercles are connected with the 

 optic nerve, with the occipital region, and with the median cor- 

 pora geniculata. 



The function of the anterior of these bodies is mainly con- 

 nected with the eye; the posterior are associated with the sense 

 of hearing. 



