288 
Proceedings of the Royal Society of Edinburgh. [Sess. 
narrow zone bordering the optic thalamus, corresponding to the external 
medullary lamina of the thalamus, which shows an abundant fine degenera- 
tion, but contains fewer coarse fibres. Fine fibres are very numerous in 
the grey matter of the optic thalamus ; they terminate chiefly in the lateral 
nucleus. Some are found in the anterior nucleus, but practically none in 
the mesial nucleus. The grey matter of the caudate and lenticular nuclei 
are quite free. Only a very few of the coarse fibres are to be found in the 
capsule behind the posterior end of the lenticular nucleus, but the fine 
degeneration extends beyond that point. 
In the lower levels of the capsule the genu and the anterior limb are 
practically free from degeneration, both coarse and fine ; it is confined 
Fig. 3.— Internal capsule, lower level. 
C.N., head of caudate nucleus. 
O.T. , optic thalamus. Cl., clau- 
strum. 
entirely to the posterior limb, and does not extend much behind the 
posterior extremity of the lenticular nucleus (fig. 3). The fine fibres are 
less numerous than in the higher levels of the capsule, but they are very 
abundant amongst the nerve cells in the lateral nucleus of the thalamus. 
In this section the posterior commissure is cut through longitudinally, but 
no fibres can be seen to pass across it to the other side. The degeneration 
shows the greatest concentration about the middle of the thalamo-lenticular 
portion of the posterior limb. On the external (lenticular) aspect of the 
capsule a few detached bundles of fibres radiate outwards, but they 
cannot be traced to their destination. No degeneration is visible in the 
grey matter of the lenticular nucleus towards which these bundles are 
directed. 
In sections through the mid-brain at the level of the third nerve root 
