Secondary Degeueraiion following Unilateral Lesions etc. ßi;-3 



posteriorly (i. e. nearest the mesencephalon). There is a slight amount 

 of fine degeneration in the grey matter of the thalamus, also most 

 abundant posteriorly. Longitudinally vA\t degenerated fibres are seen 

 passing' through the coi'pus callosum and radiating outwards into the 

 centrum semiovale of the right hemisphere, but no degeneration can 

 be made out in the right internal capsule. 



In Cat VI in coronal sections through the middle of the optic 

 thalamus the bundles of the left internal capsule contain numerous 

 uniformly scattei'ed, transversely cut, degenerated fibres, except at the 

 superior (posterior in man) extremity which is free from degeneration. 

 A slight amount of fine degeneration is present in the optic thalamus 

 just mesial to the internal capsule. No degenerated fibres cross in 

 the corpus callosum at this level (sections more anteriorly were not 

 examined), but a considerable number are visible in bundles in the 

 inferior (anterior) part of the right internal capsule. (On examining 

 the brain of this animal post-mortem, the mesial surface of the poster- 

 ior limb of the right sigmoid gyrus was found to be damaged; this 

 would account for the degenerated fibres in the right internal cap- 

 sule). In sections through the posterior part of the thalamencephalon 

 the left internal capsule (now becoming compacted to form the crusta) 

 shows marked degeneration, and from its anterior portion many fibres 

 can be seen streaming into the grey matter of the subthalamic re- 

 gion and corpus albicans of the same side. Similar fibres are given 

 off from the inferior or mesial portion of the right internal capsule 

 to end in a corresponding manner on that side. The degenerated 

 fibres on the right side are traceable to the anterior portion of the 

 mesencephalon, at which level they occupy a small area about the 

 middle of the right crusta from which many fibres pass into the sub- 

 stantia nigra. In sections posterior to this there is no trace of any 

 degeneration in the right crusta. 



In the above two, and in all the remaining fourteen animals, the 

 whole brain behind the thalamencephalon (including mesencephalon, 

 pons and medulla oblongata) cut into thin slices, and segments from 

 the cervical, dorsal, lumbar and sacral regions of the spinal cord were 

 prepared by the Marchi method. 



