CHAP. X.] OPTIC THALAMUS AND CORPUS STRIATUM. 277 



that very little light passes through or between them. Hence they 

 appear to be dark masses lying in the substance of the ganglion, 

 and, from their opacity, it is very difficult to determine their exact 

 relation to the elements of the vesicular matter. Many of the bun- 

 dles, however, appear to us to attach themselves, at different parts of 

 the ganglion, as if around a large vesicle of which, with its nucleus, 

 we have sometimes seen indications at one extremity of the dark 

 mass of aggregated fibres. Other bundles of fibres appear to 

 emerge from the corpus striatum, and to contribute to form the 

 fibrous matter of the hemisphere. 



If this view of the structure of the corpus striatum be correct, 

 it would appear, that, while a large proportion of the fibres which 

 constitute the inferior layer of the crus penetrate that ganglion, 

 many of them do not pass beyond it. They may be described as 

 terminating in it, or, more properly, if traced from above, as 

 taking their origin or point of departure from it. Many of the 

 fibres which seem to pass from the corpus striatum into the white 

 matter of the hemisphere are doubtless similarly related to the 

 former body, t. e., take their rise from the vesicular matter, or, to 

 speak more exactly, pass between the vesicular matter of the hemi- 

 sphere and that of the corpus striatum. It is also highly probable 

 that some fibres pass completely through the corpus striatum. 



Thus, three sets of fibres may be described as existing in the 

 corpus striatum ; 1st, those which below enter into the formation 

 of the crus, and above are connected with that ganglion; 2ndly, 

 those which are connected inferiorly with the corpus striatum, and 

 above with the cerebral convolutions ; and lastly, those which pass 

 from the white substance of the hemispheres through the corpus 

 striatum to the crus cerebri. And of these three sets of fibres, 

 the first serves to connect the corpora striata with the mesocephale 

 and medulla oblongata ; the second to connect the cerebral convo- 

 lutions with the corpora striata ; and the third to connect the con- 

 volutions with the mesocephale and medulla oblongata. It must 

 be confessed, however, that the evidence upon which the existence 

 of the third class of fibres rests is less satisfactory than that for 

 the first and second, although most of those anatomists who are 

 contented with coarse dissection seem to recognize only the third 

 class. 



The fibres of the optic thalamus are doubtless, also, continuous 

 with some of those which form the white matter of the hemi- 

 spheres ; and from the intimate manner in which this body is 

 embraced by the corpus striatum, and the close connexion which 



