1888.] and Distribution of the Cranial Nerves. 



sections through the rootlets of the Illrd nerve of man, beginning 

 from its exit out of the brain and passing peripheralwards, and have 

 fonnd that in the different rootlets a well-marked ganglion is formed 

 in the same way as any spinal ganglion, with, however, one important 

 difference; the nerve cells and groups of nerve cells have degenerated, 

 but their place and position remain conspicuously marked out with 

 characteristically arranged masses of peculiar neuroglia- like con- 

 nective tissue substance. So striking is the resemblance to a spinal 

 ganglion, that with a low power it is difficult at first sight to believe 

 that it is not a section of a functional ganglion which is exposed to 

 view. 



These degenerated ganglia are limited to a definite portion of each 

 nerve rootlet just as in a spinal ganglion ; centralwards of the gang- 

 lion the degenerated tissue can be traced as a strand of the same 

 peculiar neuroglia-like connective tissue into the brain ; peripheral- 

 wards of the ganglion all trace of altered nerve tissue or ganglion 

 cells has disappeared. 



Here then we have what appears to me without doubt to be the 

 phylogenetically degenerated posterior root and root ganglion of the 

 Illrd nerve ; so that in its posterior root, and in the situation of its 

 root ganglion, it conforms also to the plan of a complete spinal nerve. 



In the IVth nerve I find the same structure, an anterior root com- 

 posed of a large-fibred portion and a small small-fibred portion ; the 

 destiny of this latter, and its connexion with any vagrant motor 

 ganglion, I have not yet had time to trace out. 



Soon after the IVth nerve leaves the valve of Yieussens, it forms 

 upon it a conspicuous spinal ganglion of the same character as those 

 on the rootlets of the Illrd nerve, the cells of which are all de- 

 generated, and the degenerated posterior root fibres are conspicuous 

 between the brain and this ganglion, but cease peripheralwards of 

 the ganglion. 



In the Vlth nerve the small-fibred part of the anterior root is much 

 more doubtful than in the case of the two preceding nerves ; so, too, 

 with the posterior root, its ganglion is limited to a few degenerated 

 nerve cells, and is nothing Like so conspicuous as in the case of the 

 Illrd and IVth nerves. 



In the so-called motor root of the Vth nerve we see again distinct 

 groups of small fibres together with the large motor fibres. I have 

 not yet had time to trace out these small fibres to their respective 

 motor ganglia, but have little doubt that they will be found to bear 

 the same relation to the spheno-palatine ganglion as those of the 

 Illrd nerve do to the oculo-motor ganglion. In the so-called motor 

 root of the Vth nerve is found also a degenerated posterior root, with 

 its ganglion in the same situation and of the same character as in the 

 preceding nerves. . 



