292 PRACTICAL ANATOMY. 



gray matter. It is pear-shaped, the larger end of the pear 

 presenting forward and projecting into the anterior and 

 inferior part of the lateral ventricle. Along its upper sur- 

 face is a group of ganglionic cells called the caudate nu- 

 cleus. Within the substance of the corpus striatum is the 

 lenticular nucleus, another arrangement of ganglionic 

 nerve-cells. The corpus striatum rests on the anterior 

 portion of the crus cerebri of each side. The greater 

 portion of it is imbedded in the cerebral hemispheres, and 

 is known as the extra- ventricular portion, while that part 

 which presents within the ventricle is known as the intra- 

 ventricular portion. The tcenia semicircularis is a lon- 

 gitudinal commissure which arises anteriorly in common 

 with the anterior pillar of the fornix, and curves back- 

 ward and outward in the groove between the optic thala- 

 mus and corpus striatum, and becomes finally lost in the 

 middle cornu of the lateral ventricle. The optic tliala- 

 mus is placed behind and to the inner side of the corpus 

 striatum ; it is an ovoidal structure, and rests upon the 

 crus cerebri of each side. It is composed of an external 

 white portion and an internal mixed portion of gray and 

 white matter. A collection of ganglionic cells in the 

 interior of the optic thalamus, arranged in the form of 

 a sickle, is called the falciform nucleus. The anterior 

 extremity of the optic thalamus is pointed and forms the 

 posterior boundary of the foramen of Monro. The 

 posterior extremity is broad and rounded, and presents 

 two elevations, the external and internal geniculate 

 bodies, which are the termini of the optic tracts. The 

 upper surface is convex and rounded. Its outer portion 

 forms part of the floor of the lateral ventricle. Its inner 

 portion is covered by the fornix, from which it is sepa- 

 rated by the velum interpositum and its fringe-like 

 border, the choroid plexus. The inner surface of the 





