THE THIED, FOURTH, AND SIXTH CRANIAL NERVES. 221 



further on. The superior division of the nerve, stip. div., becomes 

 distinct from the inferior at level 40 on the millimetre scale. The 

 ciliary ganglion is situated between levels 48 and 51, and the limits 

 within which its nerve-cells are distributed are shown in the dotted 

 diagram lying by the side of the main trunk. Section (50) exhibits 

 the ciliary ganglion, the nerve-cells of which are represented by dots. 

 In sections (50) and (55) many of the terminal branches of the nerve lie 

 among the muscle fibres to which they are distributed. 



The diagram of the nerve and the millimetre scale accompanying 

 it are each magnified three diameters. The transverse sections, which 

 are cut to a thickness of 25/x,, and are stained with osmic acid, are 

 magnified sixteen diameters. 



*&' 



Fig. 2. A series of transverse sections of another right 3rd 

 cranial nerve, taken at intervals of five millimetres from its super- 

 ficial origin to the termination of its branches in the muscles to which 

 these are distributed. To the left is seen a sketch of the nerve 

 slightly magnified, accompanied by a millimetre scale, equally 

 enlai-ged, indicating the various levels at which the transverse sections 

 are made. 



In the fiirst transverse section (5) is seen the vestigial structure, 

 V.S., found in this nerve close to its superficial origin. In this and 

 the succeeding sections the position of the short root of the ciliary 

 ganglion, cil. (lang., and the superior and inferior divisions of the main 

 trunk, sup. div. and inf. div., are indicated. The two divisions of the 

 3rd nerve become distinct from one another in section (40), and the 

 short root of the ciliary ganglion has separated from the inferior 

 division, and already contains nerve-cells in section (50). In the nerve 

 here represented, the short root is unusually long ; in all the other 

 nerves examined it was so short that the ciliary ganglion was almost 

 sessile on the nerve as in the preceding figure. In section (52) the 

 ciliary ganglion is cut across and its long root is also seen. In section 

 (55) the ciliary nerves are seen, and the inferior division of the main 

 trunk has become diminished in size, having given off some muscular 

 branches. The superior division is embedded in muscle in the last 

 four, as is also the inferior division in the last section. 



The sketch of the nerve, reconstituted from the transverse 

 sections, on the left, shows the commencement of the main trunk in 

 sejDarate roots, not surrounded by a fibrous sheath, and containing a 

 vestigial structure, the size and limits of which between the limits 

 and 8 are indicated by the accompanying columns of dots tailing off 

 above and below. The dura mater surrounds the nerve for a few 

 millimetres before it finally ensheathes it at level 21. The two 

 divisions become separate at level 37, the short root of the ciliary 

 ganglion is formed at 48 and passes into the ciliary ganglion, e.g., at 

 level 51. The ganglion receives its short root at 52| and terminates 

 at 53i. By the side of the ganglion is a diagram indicating the relative 

 number and the situation of the nerve-cells in the ciliarv srano'lion. 

 its long root and the cniary nerves. The superior division is seen 

 to pass into muscle at level 50 and the inferior division at level 59. 



