THK BRAIN 



345 



ment is closely connected with it, although the thalamus always forms a 

 separate structure. The corpus striatum elongates as the cerebral hemi- 

 sphere lengthens, its caudal portion curving around to the tip of the in- 

 ferior horn of the lateral ventricle and forming the slender tail of the caudate 

 nucleus (Fig. 349). The thickening of the corpus striatum is due to the 

 active proliferation of cells in the ependymal layer which form a promi- 

 nent mass of mantle layer cells. Nerve fibers to and from the thalamus to 

 the cerebral cortex course through the corpus striatum as laminae which 



Anterior horn 



Nucleus caudatus 



Intenrntriiiilar 

 foramen 



Third ventricle 



Chorioid plexus of 

 lat. ventricle 



Posterior horn 



Lenticular nucleus 

 Ant. columns of 

 fornix 

 Internal capsule 



Thalamus 



Hippocampus 



FIG. 350. Horizontal (coronal) section through the fore-brain of a 160 mm. fetus (His). 



are arranged in the form of a wide V, open laterally, when seen in hori- 

 zontal sections. This V-shaped tract of white fibers is the internal cap- 

 sule, the cranial limb of which partly separates the corpus striatum into 

 the caudate and lenticular nuclei (Fig. 350). The caudal limb of the 

 capsule extends between the lenticular nucleus and the thalamus. 



The thalamus and corpus striatum are separated by a deep groove 

 until the end of the third month (Fig. 347). As the structures enlarge, 

 the groove between them disappears and they form one continuous mass 

 (Fig. 350). According to some investigators there is direct fusion between 

 the two. 



