222 DR J. 0. WAKELIN BARRATT. 



The transverse sections were 25ja in thickness, were stained by 

 osmic acid, and are magnified six diameters. The diagram of the 

 nerve and the milhmetre scale accompan3'ing it are each magnified 

 two and a half diameters. 



Fig. 3, a. A portion of section (5), fig. 2, more highly magnified 

 to show the arrangement of the granular material (fig. 2, v.s.), 

 exhibiting no definite structure, and often arranged in masses of 

 about the same diameter as nerve-cells (cp. fig. 3, b). It is this 

 material which is regarded as a vestigial ganglion by some observers. 

 The nerve-fibres seen in the section are mostly large medullated 

 (about 14/x in diameter), but are mixed with a few small medullated 

 fibres. Osmic acid staining. x 150. 



b. The short root of the ciliary ganglion shown in section (50), 

 fig. 2, more highly magnified to show the nerve fibres and cells. 

 The former are chiefly small medullated fibres, though a few medium- 

 sized fibres are seen, especially towards the upper part of the section. 

 Many of the fibres are cut across somewhat obliquely. Eight nerve- 

 cells are seen, in three of which the nucleus is recognisable. Osmic 

 acid staining. x 190. 



c. One of the branches of the sviperior division of the 3rd nerve, 

 taken from fig. 2, section (45), more highly magnified. The nerve- 

 fibres are mostly large medullated (12/x in diameter), but smaller 

 medullated fibres are also met with, the latter varying in number in 

 difterent situations, but generally being about one-third as numerous 

 as the former. Osmic acid staining. x 190. 



Fig. 4. A series of transverse sections of the 4th cranial nerve, 

 taken, as in figs. 1 and 2, at intervals of five millimetres from its 

 superficial origin to its termination. To the left is seen a sketch of 

 the nerve, drawn to scale, reconstituted from a complete series of 

 sections mounted at intervals of one-quarter of a millimetre. 



The first sections show the various fibrils of which the nerve is 

 made up, placed loosely side by side, but not bound together by a 

 fibrous sheath, the dura mater first investing the nerve in section (40). 

 The meningeal branch, a, is seen in sections (35) to (50). Two smaller 

 branches, b and r, are to be seen accompanying the main trunk in 

 sections (40), (45), and (50). Except in section (50), where the nerve 

 divides into two bundles, one large and one small (a similar 

 arrangement was found in another of the nerves examined in serial 

 section, but in a difterent situation), the main trunk shows little 

 tendency to break up until near its termination, in section (75). The 

 last two sections are embedded in the muscle to which the nerve is 

 distributed. At eighty-five millimetres from its commencement 

 most of the bundles into which the main trunk has divided have 

 usually already reached their termination, so that only a few nerve- 

 twigs still remain, section (85). 



The sketch of the nerve on the left exhibits its comparatively 

 simple structure. The meningeal branch, a, approaches the main 

 trunk at level 33 on the milliiuotre scale, and becomes 



