NERVOUS CENTRES. (HUMAN ANATOMY. THE ENCEPHALON.) 



699 



and to the outside of the thalamus. It is pear- 

 shaped : its thick end is directed forwards and 

 inwards, and it gradually tapers backwards 

 into a caudate process of considerable length, 

 which winds downwards, forwards, and inwards 

 into the descending cornu of the lateral ventricle, 

 at the anterior extremity of which it terminates. 

 Placed on the outside of the thalamus, it seems 

 to embrace it there, and to adhere very inti- 

 mately to it. The taenia semicircularis lies in 

 a groove between the two bodies, and as it 

 were constricts their connecting fibres. 



The corpus striatum is of a dark grey colour. 

 A considerable portion of it projects free into 

 the cavity of the ventricle, forming an extensive 

 convex surface there. The rest is firmly im- 

 bedded in the fibrous substance of the hemi- 

 sphere, and in position corresponds to the base 

 of the insula, which for that reason has been 

 called the lobule of the corpus striatum. The 

 free surface as contributing to form the ventri- 

 cular wall is covered by the lining membrane 

 of the ventricle and a layer of nucleus-like 

 particles; it is traversed by several veins. This 

 surface is limited on the outside by the plane 

 of fibres, which, after emerging from it, incline 

 inwards and contribute to form the corpus cal- 

 losum. On the inside it is limited by the tenia 

 semicircularis, which separates it from the optic 

 thalamus. That portion of the free surface 

 which is seen in the inferior horn of the ven- 

 tricle has, as already stated, the appearance of 

 a caudiform prolongation of the upper portion ; 

 this probably arises from the diminution of the 

 body in thickness at its inferior part, the portion 

 which belongs to the inferior cornu forming the 

 apex of a cone, of which the upper convex 

 portion forms the curvilinear base. 



When sections are made through the corpus 

 striatum, it is found to be traversed by very 

 numerous bundles of fibres. It is necessary 

 that these sections should be directed obliquely 

 from below upwards in a direction parallel to 

 the inferior layer of the crus cerebri. The 

 bundles are thicker and more closely approxi- 

 mated to each other inferiorly; but as they 

 ascend, they diverge, and radiate, some for- 

 wards, others outwards, and others backwards ; 

 some pass nearly vertically upwards. A section 

 made quite in the horizontal direction cuts all 

 these fibres more or less transversely, so that 

 the cut surface presents a grey colour inter- 

 spersed with white spots of variable size, ac- 

 cording as the bundles have been cut trans- 

 versely or obliquely ; but when the section is 

 made in the oblique direction, as above di- 

 rected, then the surface presents a striated ap- 

 pearance like numerous and regular white 

 veins in a dark marble, the bundles of fibres 

 being cut lengthways. 



In tracing the bundles of fibres through the 

 corpus striatum, we find that they divide and 

 subdivide and occasionally anastomose. Each 

 subdivision becomes clothed as it were with 

 grey matter, which fills up the space between 

 it and the adjacent ones. The grey matter en- 

 sheathes these bundles of fibres, as the areolar 

 tissue does the fascicles of coarse muscles, and 



it may be dissected away from them, as we 

 remove the areolar tissue from the muscular 

 bundles. 



It is an important problem to determine the 

 exact source of these fibres and their precise 

 destination. There can be no doubt that many 

 of them are continuous with the inferior plane 

 of the crus cerebri. Of those, the major part 

 are usually supposed to pass through to the 

 white substance of the hemisphere, and some 

 no doubt proceed no farther than the corpus 

 striatum. The other fibres which are found in 

 this body may be viewed as taking their point 

 of departure from its vesicular matter, and 

 radiating, some outwards into the centrum 

 ovale, others backwards to the optic thalamus, 

 forming a bond of connection with that body. 

 It must be borne in mind that, as the corpus 

 striatum is a body of considerable thickness, 

 these fibres which emerge from it must pro- 

 ceed in very different planes and with varying 

 degrees of obliquity. Other fibres are found 

 in the corpora striata, which however do not 

 contribute to its striation. These are the fibres 

 of the anterior commissure. 



From a comparison of the small amount of 

 fibrous matter in the inferior plane of the crus 

 cerebri with the immense mass which forms 

 the white substance of the hemispheres, (even 

 if we exclude those fibres which form com- 

 missures,) it is impossible to suppose that the 

 latter is derived from the former only; nor, 

 indeed, can it be admitted that even the greater 

 part of the fibrous matter of the hemispheres 

 is continuous with that of the crura, whether 

 on their superior or inferior plane. A con- 

 siderable portion of them doubtless, when traced 

 from the hemispheres downwards, will be 

 found not to pass below the corpora striata 

 or optic thalamus. 



We may regard the corpus striatum as a 

 mass of grey matter with fibres implanted 

 in it which connect it with the other parts 

 of the encephalon. These parts are, 1st, the 

 hemispheres ; 2d, the optic thalami ; 3d, the 

 crura cerebri, mesocephale, and medulla ob- 

 longata. Of the?e last fibres it is probable, 

 (but I am disposed to think far from certain,) 

 that some of those which form the inferior 

 layer of the crus pass through the corpora 

 striata, and diverge among the other fibres of 

 the centrum ovale. 



Thus the corpora striata are connected to the 

 optic thalami by fibres which pass from their 

 concave or inner border to those bodies; to the 

 convolutions of the brain by fibres continuous 

 with some of those which form the white sub- 

 stance of the hemisphere, and we have seen 

 that the convolutions of the imula have a very 

 close relation to them; to the mesocephale and 

 medulla oblongata by the fibres which form the 

 inferior layer of the crus; and to each other by 

 those which, emerging from them, contribute 

 to form the corpus callosum, and also by the 

 anterior commissure. 



The vesicular matter of the corpora striata 

 does not differ from that of the convolutions. 

 It is traversed by a multitude of fibres. These, 



