THE THIRD, FOURTH, AND SIXTH CRANIAL NERVES. 217 



ganglion are similar to those in the short root, small medullated 

 fibres, 3/x to 4/a in diameter, largely preponderating. It must 

 be borne in mind, however, that the size of the nerve-fibres, as 

 also of the nerve-cells, is influenced by any stretching to 

 which the main trunk and its branches may have been sub- 

 jected prior to hardening, and also by the methods of harden- 

 ing, cutting, and mounting employed. The same remark applies 

 also to the measurements given of the fibres of the 4th and 

 6th cranial nerves. 



The nerve-cells of the ciliary ganglion (fig. 3, h) are 30/x to 45/x 

 in diameter. They contain a large nucleus and nucleolus, have 

 a fairly even outline, are surrounded by a multi-nucleated capsule, 

 and in their general aspect resemble the cells of the ganglia of 

 the 9th and 10th cranial nerves, and, like these, are, as 

 already mentioned, not confined to the region in which a visible 

 swelling is present, but extend backwards along the short root 

 and forwards along the ciliary nerves, as indicated in the 

 diagrams in figs. 1 and 2, so that our conception of this ganglion 

 formed from the study of transverse sections becomes more 

 complex than that afforded by ordinary dissection. 



The chromophile material of the cell bodies is shown by 

 Nissl's method to be diffused in a pulverulent form, with a 

 tendency to a concentric arrangement about the nucleus. 

 Pisment is also found in certain cases in the cell bodies. 



The collections of amorphous granular material found in the 

 nerve near its superficial origin (fig. 1, vest. str. ; fig, 2, v.s. ; 

 fig. 3, a) resemble in size and arrangement collections of nerve- 

 cells very closely. Their existence has been long known,^ and 

 they have been regarded as vestigial in nature. Gaskell,- from 

 a study of ancestral development, regards them as representing 

 anterior root ganglia, and gives the same interpretation to the 

 finely fibrillar material which he has also found in a similar 

 situation in the 4th, 5th (motor), 6th, and 7th cranial nerves. 

 It is interesting to note that this material is situated towards 



1 Thomsen, " Uebev eigenthiimliche aus veriiiiderten Ganglienzelleu hervor- 

 gegangene Gebilde in den Stiimmen der Hirnnerven des Menschen '' (one plate), 

 Virch. Arch., B. eix. S. 459. This author describes these structures in the 3rd, 

 6th, and 7th, but not in the 4th, cranial nerves. 



- " On the relation between the structure, function, distribution, and origin of 

 cranial nerves," etc., Journ. of Physiol., 1889, x. pp. 153-211. 



