RECURRENT BRANCHES OF ABDUCENS NERVE 377 



making their presence difficult to detect; in fact, the roots may 

 run in the walls of these vessels for a considerable distance. 

 The not uncommon shrinkage of the brain in preservation may- 

 break the small abducens roots and make their connections 

 uncertain. Another consideration is that in the usual recon- 

 struction of the cranial nerves as seen from the side the abducens 

 is partially hidden by the large ganglion of the trigeminal and 

 by the otocyst and its attendant ganglia, and therefore perhaps 

 not so much an object of study as the other nerves. Finally, 

 it may be possible that the human embryos of this collection are 

 too few to justify any statements as to the frequency of the 

 presence of these recurrent branches, and that with a wider study 

 a much smaller percentage would be obtained. 



Considerable variation in the exact origin and course of the 

 recurrent branches is found, but it is possible to designate certain 

 types into which all may be grouped. In their method of origin 

 from the medulla floor they may arise with the main abducens 

 roots, some of the fibers from the same roots pointing caudally, 

 some curving sharply forward, so that there is a crossing of the 

 individual bundles in the same roots; or the recurrent nerves may 

 arise by one or more separate roots, closely caudal to the last 

 abducens root. The usual course is ventral and lateral toward 

 the jugular foramen, with the vagus and glossopharyngeal nerves, 

 but some pass laterally, to the dDrsal musculature of the neck, 

 while others turn dorsally, as in the cases described by Barni- 

 ville and by me formerly, to end beside the more dorsal part of 

 the hind brain. It is quite common to find the recurrent branch 

 doubled on one or both sides of an embryo, as in figure 1, and, 

 as is shown there, the two branches may be joined at some 

 distance from the brain wall. In size there is again great vari- 

 ation; some recurrent nerves are of a few fibers only, others as 

 large or larger than the abducens itself; frequently the large 

 branches end in terminal expansions. In length they also vary, 

 some running only a few micra, others extending past the vagus 

 nerve far ventrally or far laterally to the musculature, as has 

 been noted. 



