THE CEREBRAL HEMISPHERES 



675 



curves downward and forward into the pyriforni lol)e. The roof of the ventricle 

 is formed by the corpus callosuni and tlie inner wall is the septum pellucidum. 

 After removal of the roof the floor is seen to l)e formed chiefly by two bodies. The 

 anterior one is the caudate nucleus (Nucleus caudatus), a somewhat pear-shaped 

 gray eminence, the long axis of which is directed obliciuely upward, backward, and 

 outward. Its anterior large end is termed the head, and the i)osterior long tapering 

 end the tail. The posterior body, the hippocampus, is white on its ventricular 

 surface, which is strongly convex. It curves outward and backward and then turns 

 downward and forward to join the pyriform lobe. The two bodies are separated 

 by an oblique groove which is occupied by the chorioid plexus of the lateral ven- 

 tricle. This is the thickened edge of a fold of pia mater, the tela chorioidea (or 

 velum interpositum), which lies between the hippocampus and the thalamus. It 

 contains convolutions of small blood-vessels and in old subjects there may be 

 calcareous concretions in it. The plexuses of the two sides are continuous through 

 the interventricular foramen. On drawing the chorioid plexus backward a narrow 



Fig. 513. — Sagittal Section of Brain of Horse. 

 Section is cut about 1.5 cm. to the right of the median plane. M, Medulla oblongata; P, pons; P.c. (above 

 M), chorioid plexus of fourth ventricle; Cm., central white matter (corpus medullare) of cerebellum and of cere- 

 brum; P.c. (in front of P), cerebral peduncle; H, hippocampus; V, lateral ventricle; T, tlialamus; N.c, caudate 

 nucleus; C.i., internal capsule; N.I., lenticular nucleus; B.o., olfactory bulb. 



white band, the stria terminalis (or taenia semicircularis) , is seen along the margin 

 of the caudate nucleus, wliere it bounds the intermediate groove. The plexus 

 partially covers a wider white band which is blended with the white substance of 

 the hippocampus; this is the posterior pillar of the fornix and its continuation, 

 the fimbria. 



The corpus striatum' is the great basal ganglion of the hemisjihere. It is 

 situated in front of the thalamus and the cerebral peduncle, and its anterior rounded 

 end appears on the base of the hemisphere at the trigonum olfactorium. It is 

 composed of two masses of gray matter, the caudate and lenticular nuclei, separated 

 incompletely by tracts of white matter which are known collectively as the internal 

 capsule. The caudate nucleus (Nucleus caudatus) is the dorso-medial and larger 

 of the two gray masses ; it has been seen in the examination of the floor of the lateral 

 ventricle. The lenticular nucleus (Nucleus lentiformis) lies ventro-laterally, over 

 the trigonum olfactorium and the fossa transversa. It is related externally to a 

 layer of white matter termed the external capsule, which separates it from a stratum 

 of gray substance known as the claustrum. The two nuclei are fused in front, and 



' The term arose from the striated appearance of the mass in sections cut in certain planes, 

 the gray matter being cut up into strands by tracts of wliite fibers. 



