2/0 Journal of Comparative Neurology. 



granules and eccentricity of nucleus when I could not find an 

 obvious traumatic lesion of the neurites. Whether all the cere- 

 bral afferent neurones for the spinal segments have their cell- 

 bodies ' centralized ' in the nuclei of Goll and Burdach, and 

 which cells of the nuclei of afferent cranial nerves are cerebral 

 afferent and which ones are simply ' intermediate ' is hardly 

 possible to say now ; nor is it certain whether we can distin- 

 guish the cerebellar afferent neurones from them simply by a 

 study of Nissl specimens. The external nucleus of Burdach is 

 most probably a pure cerebellar ' Anteil '; but there is no 

 marked peculiarity of its cells, except perhaps in their greater 

 resemblance with those of the nucleus lateralis, in size as a 

 whole and of the granules. 



We have seen that the cerebral afferent apparatus consists 

 of two sets of neurones, one terminating in the thalamus and 

 one arising there. This same plan holds not only for the com- 

 mon sensory-motor cerebral apparatus, but also for the visual- 

 motor and the other special mechanisms. Since the optic ap- 

 paratus is the best known, it may find a place here especially 

 because in its literature we find splendid illustrations of general 

 and experimental pathology. 



The retina consists of three layers of neurones: i. The 

 rods and cones, 2. the intermediate layer, and 3. the ganglion- 

 cell layer ; between the first and the second and the second and 

 the third, there are 'molecular layers,' i. e. tissue composed of 

 the end-fibrils of the cells of these layers. The ganglion-cells 

 give rise to fibers which help to form the optic nerve and tract 

 and terminate in the external geniculate body, the pulvinar and 

 to a lesser extent, in man at least, the anterior corpus quadri- 

 geminum. Among the cells located among these 'primary 

 terminations ' there are some which belong to the cerebral af- 

 ferent neurones ; especially most of the cells of the external 

 geniculate body belong in this category ; their neurites form 

 the ' optic radiation ' and terminate in the visual area. We saw 

 in the introduction^ the very interesting differences of degener- 



» See p. 118. 



