214 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



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. 97). 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 per- 

 haps regard the corpus as a means by which the functional 

 activities of the two sides of the cerebrum are associated. 



The Corpora Striata and Optic 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 external 

 geniculate bodies form part of the optic path. In addition, how- 

 ever, 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 

 optic thalami have been frequently studied experimentally to as- 

 certain whether they have specific functions independently of their 

 relations to the cortex. These efforts have given uncertain results. 

 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. Lesions of the nucleus caudatus are said 

 to be accompanied always by a rise in body temperature and an 

 increase in heat production, and stimulation of the same nucleus 

 gives a very marked rise in blood-pressure. These facts indicate 

 a possible connection of this nucleus with heat and vasomotor 

 regulation. Other observers have supposed that these nuclei are 

 especially concerned in the co-ordination of the muscules concerned 

 in involuntary or unconscious movements. On the anatomical side 

 we have the striking fact that the nuclei of the corpora striata 

 have few connections with the cortex, but, on the other hand, 

 send an independent system of projection fibers into the brain stem. 

 Embryologically these structures are developed from the wall of 

 the forebrain and would seem to have a physiological importance 

 similar to that of the cortex itself, but experimental and clinical 

 facts are at present insufficient to justify any hypothesis as to their 

 special functions. With regard to the various nuclei of the optic 

 thalamus it is known that they form abundant connections with 

 the sensory areas of the cortex cerebri, and from this standpoint 



