232 NERVOUS SYSTEM. [SECT. 115. 



While it is comparatively easy to ascertain, at least in its prin- 

 cipal features, the structure of the corpora striata, it is far other- 

 wise with the optic thalami and corpora quadrigemina, and chiefly 

 because the nerve-fibres are less disposed in bundles, but more 

 isolated and most intimately mingled with the grey substance, 

 and, consequently, cannot be followed for any great length. In 

 this situation, however, the investigation of the grey substance is 

 perfectly easy, and its elements, the nerve-cells, present nothing 

 that is peculiar, except that, in the optic thalami, they are, for the 

 most part, deeply coloured ; those of the corpora quadrigemina 

 are, on the other hand, pale. With regard to the nerve-fibres, it 

 is certain that the upper part of the cerebral peduncle, i. e., the 

 crura cerehelli ad corpora quadrigemina (the continuations of the 

 olivary columns, part of the restiform bodies and the eminentice 

 teretes), enter the ganglia in question ; still I have not, hitherto, 

 succeeded in ascertaining anything definite about their course. I 

 believe I am warranted in stating, that at least the greater part of 

 these bundles do not pass into the medullary substance of the 

 hemispheres, because, on the one hand, the most of the fibres fall 

 from their original diameter of o - ooi2'" to o'oo4'", o'ooi'", and 

 less; and, on the other, no trace of such a transition is found on 

 the side of the optic thalamus, which is directed towards the 

 medullars substance. 



The superficial white covering of the ganglia in question is, 

 however, to be excepted, which, at any rate, may establish a con- 

 nection between them and the hemispheres, as its fibres, of cool'" 

 to 0003'", or even more, being arranged in bundles, and decussating 

 horizontally in various directions, do not appear to terminate in 

 the thalami. In like manner, the relation of the optic nerves 

 to the optic thalami and corpora quadrigemina, and of the 

 fornix to the latter, is not well made out, so that it is the more 

 satisfactory, at all events, to be able to answer, with some degree 

 of certainty, another important question. If the outer part of the 

 optic thalamus be examined, it is found that it adjoins a consider- 

 able mass of Avhite substance, which, at first sight, appears as a 

 continuation of the base of the cerebral peduncle, passing ex- 

 ternally and inferiorly upon the optic thalami, between the lenti- 

 cular and caudate nuclei of the corpus striatum, to enter directly 

 the medulla of the hemispheres. On closer inspection, it is seen 

 that the white substance, as was mentioned above, in part enters 

 into the corpora striata, particularly into the lenticular nuclei; in 

 part radiates from without inwards, from the hemispheres into the 



