262 



THE NERVOUS SYSTEM 



ing the thalamus and caudate nucleus from its medial surface. It is then seen 

 to bear the imprint of both of these nuclei, and especially of the thalamus; and 

 between the two impressions it presents a prominent curved ridge (Fig. 195). 

 This ridge is responsible for the sharp bend known as the genu, which is evi- 

 dent in horizontal sections at appropriate levels through the capsule. Many 

 broken bundles of fibers, representing the thalamic radiation, are seen enter- 

 ing the capsule upon its medial surface. 



THE CONNECTIONS OF THE CORPUS STRIATUM AND THALAMUS 



What is the function of the corpus striatum, and what connection does it 

 have with other parts of the nervous system? These questions, to which no 



Caudate nucleus 



Parietal stalk of thalamus 

 Corticospinal tract 



Insula 

 Claustrum 



Putamen 



Globus pallidus 

 Ansa peduncularis 

 Red nucleus 



\ )\ ;^x>\ 



Ansa lenticularis 

 Substantia nigra 

 Hypothalamic nucleus 



Fig. 196. Diagram of the connections of the caudate and lenticular nuclei. 



final answer can as yet be given, have recently become of great importance, 

 because of the frequency with which degeneration of the lentiform nucleus has 

 been found at autopsy in patients who have shown serious disturbances of the 

 motor mechanism (Wilson, 1912-1914). It seems probable that the corpus 

 striatum exerts a steadying influence upon muscular activity, the abolition of 

 which results in tremor during voluntary movement. The probable connec- 

 tions of the corpus striatum are indicated in Fig. 196. Striopetal fibers reach 

 the caudate nucleus from the anterior and medial nuclei of the thalamus (Sachs, 

 1909). According to Cajal, the corpus striatum also receives collaterals from 

 the corticospinal tract. Internuncial fibers join together various parts of the 

 corpus striatum. The majority of these seem to run from the caudate nucleus 



