THE CORPORA QUADRIGEMINA 259 



of the fibers from the motor cortical zone pass to or through 

 the corpus striatum. This may be only a relay station, and 

 the corpus may be quite subsidiary. It undoubtedly, how- 

 ever, is connected with motion in some way. 



The precise function of the optic thalami is equally ob- 

 scure. The relation of these organs to the tegmenta would 

 suggest that they have something to do with the sensory 

 fibers on their way to the cortex. It cannot be denied that 

 they are concerned in sensation, since their removal is fol- 

 lowed by crossed anesthesia. They may likewise be relay 

 stations. Each sends fibers to the 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 upward 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 s*ome 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 divi- 

 sion are followed by anesthesia; and that lesions affecting 

 the entire posterior limb are followed by both paralysis and 

 anesthesia 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 pos- 

 terior limb of the capsule. 



Nothing conclusive can be said about the function of the, 

 external capsule or of the claustrum. 



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



