228 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



results of histological studies, which indicate that the fibers of the 

 corpus callosum do not enter directly into the internal capsules, 

 to be distributed to underlying portions of the brain, but are truly 

 commissural and connect portions of the cortex of one hemisphere 

 with the cortex of the other side. This relation is indicated in the 

 accompanying diagram (Fig. 102). So far as the motor regions are 

 concerned, there is some evidence that the connection thus es- 

 tablished is between symmetrical parts of the cortex (Muratoff) — 

 that is, between parts having similar functions — and we may 

 regard the corpus as a means by which the functional activities 

 of the two sides of the cerebrum are associated. 



The Corpora Striata and Thalami. — The numerous masses 

 of gray matter found in the cerebrum beneath the cortex, 

 in the thalamencephalon, and in the midbrain have each, of 

 course, specific functions, but, in general, it may be said that 

 they are intercalated on the afferent or efferent paths to or from 

 the cortex. Their physiology is included, therefore, in the 

 description of the functions mediated by these paths. For 

 instance, the lateral geniculate bodies form part of the optic 

 path. In addition, however, these masses of cells contain 

 in many cases reflex arcs of a more or less complicated kind, 

 through which afferent impulses are converted into efferent 

 impulses that affect the musculature or the glandular tissues 

 of the body. The large nuclei constituting the corpora striata 

 (nucleus caudatus and n. lenticularis) and the thalami have 

 been frequently studied experimentally to ascertain whether 

 they have specific functions independently of their relations to 

 the cortex. Older experiments (Nothnagel), in which the attempt 

 was made to destroy these nuclei by the localized injection of 

 chromic acid, are probably unreliable, as the destruction involved 

 also the projection fibers passing to the cortex. More recent work 

 has seemed to indicate quite specific functions for these structures. 

 The optic thalamus is intercalated on the sensory paths and plays 

 an important part in correlating the activity of the afferent system. 

 The corpus striatum, on the contrary, has motor functions. The 

 nuclei of the corpus striatum (the nucleus caudatus, the globus 

 pallidus, and the putamen) are not connected directly with the 

 cortex of the cerebrum, although there are indirect connections 

 through the thalamus; but they are connected with the red nucleus 

 and thus brought into relation with the motor system to the cord 

 known as the rubrospinal tract. Lesions of the nucleus caudatus 

 are accompanied by marked disturbances in heat regulation, so 

 that many authors assume the existence of a heat-regulating center 

 in this nucleus. Others have suggested that the corpus striatum 

 constitutes a regulating center for the control of the more primitive 



