222 



ELEMENTS OF MAMMALIAN ANATOMY 



line than the caudal })ortions, which curve laterad around the 

 optic thalami (Fig. 107). They form a part of the floor of the 

 lateral ventricles, and are pierced by the anterior commissure 

 (Fig. 109), a small cord of white fibers. 



The corpus striatum consists of both white and gray matter. 

 The latter,' composed of cells, is disposed in two chief nuclei or 

 masses, known as the nucleus caiidatus, lying anterior and nearer 

 the median line than the nucleus lenticularis, which is more lateral 



an 



Fig. 109. — Cross-section of the Brain through the Anterior Commissure. 

 an. Arachnoid; ce, external capsule; cl, corpus callosum; cm, anterior com- 

 missure; jxc, falx cerebri; /, great longitudinal fissure; fx, columns of the fornix; 

 iCy internal capsule; «, radiating fibers of callosum; in, septum pellucidum; nc, 

 nucleus caudatus of corpus striatum; I, nucleus lenticularis; p, pia mater; vis, 

 superior longitudinal sinus; vn, third ventricle; v, lateral ventricle. 



and caudal (Fig. 109). The center of the nucleus lenticularis is 

 laterad of the optic thalamus and dorsad of the crus cerebri. A 

 thin layer of white matter, the lamina semicircularis, separates 

 the optic thalamus from the nucleus caudatus. A few fibers 

 from the cerebral peduncles form the lamina semicircularis, 

 whose edge may be seen in the floor of the lateral ventricle on 

 the lateral boundary of the nucleus caudatus. A group of fibers, 

 known as the internal capsule, separates the thalamus from the 

 nucleus lenticularis, laterad of which is the external capsule, a 

 group of fibers probably descending from the cells of the cerebral 

 cortex. The two nuclei of the corpus striatum are connected 

 by fibers, and other fibers connect these nuclei w^ith the cortex 

 of the cerebrum and the optic thalamus. 



