THE THIRD, FOURTH, AND SIXTH CRANIAL NERVES. 215 



Four of the nerves thus sectioned are represented m figs. 1, 2, 

 4, and 5, In addition to these, a large number of nerves and 

 ciliary ganglia have been examined in simple transverse and 

 longitudinal section, in respect of various details of structure. 



The Third Cranial Nerve. 



The 3rd cranial nerve (figs. 1 and 2) at its origin consists 

 of numerous fine roots, which, though in contact with each 

 other, are not closely bound together, and can be readily sepa- 

 rated. Mixed with the nerve rootlets are little collections of 

 granular amorphous material (fig. 1, vest. str. ; fig. 2, v.s.) 

 which are found to be situated chiefly towards the inner aspect 

 of the nerve trunk, and which extend from its origin onwards for 

 a distance of about eight millimetres (see sketch of nerve to 

 left, figs. 1 and 2). These are further described in a subse- 

 quent paragraph. 



The nerve is invested by the arachnoid coat at fifteen to 

 twenty millimetres from its superficial origin, and by the dura 

 mater at twenty to twenty-five millimetres from its origin. 

 The latter surrounds the nerve loosely for a short distance 

 before eusheathing it. The main trunk remains without giving 

 off or receiving any branches until it is leaving the cavernous 

 sinus,^ when it divides at about thirty-seven millimetres from 

 its superficial origin (figs. 1 and 2) into superior and inferior 

 division, both of which at a lower level break up into numerous 

 branches, which become embedded in the muscles to which they 

 are distributed. The inferior division of the 3rd nerve gives 

 off the short root of the ciliary ganglion at level forty-eight on 

 the millimetre scale, fig. 1, and at nearly the same level in fig. 

 2. The cihary ganglion is one to two millimetres long, and is 

 met with at about fifty-two and a half millimetres from the 

 superficial origin of the nerve. Not only the ganglion itself, but 

 also its short root and the ciliary nerves contain ganglion cells. 

 These are indicated in number and distribution by the dotted 

 diagram lying to the left of the sketch of the 3rd nerve shown 



1 According to the description of this nerve given in text-books of anatomy, it 

 communicates in the cavernous sinus witli the cavernous plexus, and also receives 

 a communicating branch from the first division of the fifth. I have not been 

 able to confirm this statement by a stmly of transverse sections. 



