BASAL GANGLIA 699 



Dissection. — The j^tudeut should .slice away the left hemisphere and expose the lateral veii- 

 tricle of that side, leavitifr the central injitioii of the corpus callosum in situ for the present. He 

 .should then make a series of horiz(jntal sections throULdi the island of Reil and corpus striatum of 

 tlie left .side. If he has carried out the di.ssection as recommended on the right side, he will now 

 be in a position to study the corpus striatum both in horizontal and vertical section, and at the 

 same time to examine its intraventricular part more fully. The hoiizontal sections will ]iass 

 through both nuclei of the corpus striatum with the inner and outer cap.sules, the claustrum, and 

 a portion of the optic thalamus (tig. 41 U). 



Basal Ganglia of the Hemispheres 



A series of ganglionic masses is placed in the base of each cerebral hemisphere. 

 They are subjacent (with the exception of the amygdaloid nucleus) to the island of 

 Reil and form, with that lobe, the oldest part of the hemisphere; that is to say, 

 they constitute the portion which is (as already mentioned) the first to appear both 

 in the vertebrate series and also in the development of the individual. They are 

 all semi-detached local thickenings of the grey cortex, and may be enumerated as 

 follows: — the corpora striata, each composed of tAvo nuclei, the nucleus caudatus 

 and the nucleus lenticularis; the claustra, and the amygdaloid nuclei. The optic 

 thalami are in close proximity to the corpora striata, but belong to the thalam- 

 encephalon. Certain important fasciculi of white matter are intimately related 

 to the corpora striata. The chief of these white fasciculi are the inner and outer 

 cai>sules, the anterior commissure, and the taenia semicircularis. 



The nucleus caudatus is an elongated mass of grey matter somewhat resem- 

 bling a pear with a long curved stalk. It presents a free, or ventricular, surface, and 

 a surface which is embedded in the hemisphere. It is thickest at the anterior end. 

 or head. The free surface of the anterior thickened portion looks upwards and 

 inwards, and bulges into the anterior horn of the lateral ventricle. Thence it 

 ascends with an inclination outwards to the body of the ventricle, where it forms 

 the outermost constituent of the floor of that cavity, and narrows into the com- 

 mencement of the tail. In this situation it is separated from the oj^tic thalamus by 

 the lamina cornea and tsenia semicircularis. The tail of the nucleus caudatus then 

 passes into the descending cornu. It is placed at first in front of the cornu, after- 

 wards forms part of the roof of that cavity, and ends at the amygdaloid tubercle. 

 The deep surface of the caudate nucleus is separated from the nucleus lenticularis 

 b\' a layer of Avhite matter called the inner capsule. The two nuclei are, however, 

 connected by bands of grey matter which intersect the fibres of the anterior limb 

 of the inner capsule, and they are directly continuous for a short distance in front. 



The nucleus lenticularis is embedded in the substance of the hemisphere 

 except at the base of the brain, where it comes to the surface for a small part of its 

 extent at the anterior perforated space. Here it is continuous externally Avith the 

 claustrum and, as before stated, with the nucleus caudatus. In horizontal section 

 it appears like a bi-convex lens, with its surface directed outwards and inwards, the 

 outer surface forming a curve of larger radius than the inner. In sagittal section 

 the lenticular nucleus is also somewhat lens-shaped in outline (fig. 417). In 

 coronal sections through the anterior part it appears crescentic, with the convexity 

 turned downwards ancl outwards (fig. 415); but in successive sections taken from 

 before backwards the crescentic gives place to a triangular or wedge-shaped outline 

 (fig. 421). In fresh brains this grey mass can be seen to he traversed by thin 

 white intersections, the internal and external medullary laminae, which divide it 

 into three zones. The middle and inner zones are of a yellowish grey colour, and 

 constitute the globus pallidus. The outer zone is of a darker reddish grey, and is 

 traversed with fine white .'Jtriie. It is called the putamen. 



The putamen is the longest part of the lenticular nucleus, and is the only portion of that 

 body which is continuous with the caudate nucleus. 



The above agrees substantially with the account which is given by Schwalbe ; this anato- 

 mist, however, describes the amygdaloid nucleus as discontinuous with the tail of the caudate 

 nucleus. According to Foster and Sherrington, the globus pallidus of the lenticular nucleus as 

 well as the putamen is continuous with the caudate imcleus. 



A band of white fibres, the ansa lenticularis, passes inwards below the inner capsule. It 

 emerges from the under surface of the lenticular nucleus, being continued from the medullary 



