THE INTERNAL CONFIGURATION OF THE CEREBRAL HEMISPHERES 263 



to the putamen, on the one hand, and from the putamen to the globus pallidus 

 on the other. The striofugal fibers arise, for the most part at least, in the globus 

 pallidus. They are collected into a bundle of transversely directed fibers, known 

 as the ansa lenticularis (Fig. 188), which is distributed to the thalamus, red 

 nucleus, hypothalamic nucleus, and substantia nigra. Other fibers belonging 

 to the same general system break through the ventral third of the internal 

 capsule to reach the thalamus (Wilson, 1914). The importance of the connec- 

 tion with the red nucleus is obvious, since by way of the rubrospinal and rubro- 

 reticular tracts the corpus striatum is able to exert its influence upon the pri- 

 mary motor neurons of the brain stem and spinal cord. The fibers to the sub- 

 stantia nigra have already been mentioned under the name strionigral tract 

 (p. 164). The impulses which travel along them are, in all probability, re- 

 layed through the substantia nigra to lower lying motor centers, although the 

 functions and connections of this large nuclear mass are still obscure. 



The Thalamic Radiation. We are now in position to understand the course 

 and distribution of the fascicles, which unite the thalamus with the cerebral 

 cortex and which consist of both thalamocortical and corticothalamic fibers. This 

 thalamic radiation may be divided into four parts: the frontal, parietal, occip- 

 ital, and ventral stalks of the thalamus, which will now be traced as fasciculi, 

 without reference to the direction of conduction in the individual fibers. 



The ventral stalk, or inferior peduncle of the thalamus, streams out of the 

 rostral portion of the ventral thalamic surface and is directed lateral ward under 

 cover of the lentiform nucleus. Some of these fibers belong to the ansa lentic- 

 ularis and run from the lentiform nucleus to the thalamus. The others, form- 

 ing a bundle known as the ansa peduncularis , runs lateralward ventral to the 

 lentiform nucleus and are distributed to the cortex of the temporal lobe and 

 insula (Fig. 196). 



The frontal stalk, or peduncle of the thalamus, consists of fibers which run 

 through- the anterior limb of the internal capsule from the lateral thalamic 

 nucleus to the cortex of the frontal lobe (Fig. 193), and in small part to the cau- 

 date nucleus also. 



The parietal stalk, or peduncle, emerges from the lateral surface of the 

 thalamus, and runs through the posterior limb of the internal capsule in close 

 association with the great motor tracts (Figs. 193, 196). It connects the lateral 

 nucleus of the thalamus with the cortex of the parietal and posterior part of the 

 frontal lobe. 



Many of these fibers, especially those terminating in the posterior central 



