792 NERVOUS SYSTEM OP THE HORSE ' 



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

 shaped gray eminence, the long axis of which is directed obliquely upward, back- 

 ward, and outward. Its anterior large end is termed the head (Caput nuclei 

 caudati), and the posterior long tapering end the tail (Cauda nuclei caudati). "The 

 posterior body, the hippocampus, is white on its ventricular surface, which is 

 strongly convex. It curves outward and backward and then turns ventrally and 

 forward to join the piriform lobe. The two bodies are separated by an oblique 

 groove which is occupied by the chorioid plexus of the lateral ventricle (Plexus 

 chorioideus ventriculi lateralis) . This is the thickened edge of a fold of pia mater, 

 the tela chorioidea of the third ventricle, which lies between the hippocampus and 

 the thalamus. It contains convolutions of small blood-vessels, and in old subjects 

 there are often calcareous concretions in it. The plexuses of the two sides are 

 continuous through the interventricular foramen. On drawing the chorioid plexus 

 backward, a narrow white band, the stria terminalis/ is seen along the margin of the 

 caudate nucleus, where it bounds the intermediate groove. The plexus partially 

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

 campus; this is the cms of the fornix and its continuation, the fimbria. 



The corpus striatum^ is the great basal ganglion of the hemisphere. It is sit- 

 uated 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 was seen in the examination of the lateral ventricle. 

 The lenticxxlar nucleus (Nucleus lentif ormis) lies ventro-laterally, over the trigonum 

 olfactoriiun and the fossa lateralis. It is related externally to a layer of white 

 matter termed the external capsule (Capsula externa), which separates it from a 

 stratum of gray substance known as the claustrum. The two nuclei are fused in 

 front, and further back they are connected by strands of gray matter which inter- 

 sect the internal capsule. 



The amygdaloid nucleus (Nucleus amygdalae) (Fig. 637) is an ovoid mass of 

 gray matter lateral to the ventral horn of the lateral ventricle and ventral to the 

 posterior part of the lenticular nucleus. Some fibers of the stria terminalis are 

 connected with it. 



The internal capsule (Capsula interna) is a broad band of white matter situated 

 between the thalamus and caudate nucleus medially and the lenticular nucleus 

 laterally. A sagittal section through the brain (Fig. 644) shows that it is in great 

 part directly continuous with the basis or ventral part of the cerebral peduncle. 

 It contains most of the so-called projection fibers of the hemisphere, which con- 

 nect the cerebral cortex with nuclei of other and more posterior parts of the brain. 

 When the fibers of the internal capsule are traced forward it is evident that they 

 spread out in all directions to reach the cerebral cortex. This arrangement, in 

 which the fibers of the corpus callosum participate, is termed the corona radiata. 



The internal capsule also contains fibers which connect the corpus striatum with the thala- 

 mus. These are termed the thalamo-striate and strio-thalamic fibers respectively, according to 

 the direction in which they conduct impulses. 



The fibers of the stria terminalis connect the amygdaloid nucleus with the septum pelluci- 

 dum and trigonum olfactorium. It is therefore probably part of the complex connections be- 

 tween the primary and secondary olfactory centers. 



Blood-vessels of the Brain. — The arteries which supply the brain are derived 

 chiefly from the internal carotid and occipital arteries. The basilar artery, formed 

 by the union of the right and. left cerebral branches of the occipital artery, enters 



1 Formerly termed the taenia semicircularis. 



^ 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 white fibers. 



