VAGUS NERVE OF THE TURTLE 307 
trunk in the upper part of the neck, but the latter is readily 
distinguished as a separate fascicle in cross sections of the com- 
mon nerve trunk at this level. In figure 3 the hypoglossal (6), 
and the small fascicle, the descendens hypoglossi, which the 
hypoglossal derives from the first cervical (a) are represented 
darker than the other fascicles of the trunk. This darker 
appearance in osmic sections is due to the fact that these fascicles 
are composed chiefly of large myelinated fibers. The descendens 
Fig. 3 Section of the vagus and hypoglossal nerves at the level indicated by 
3, figure 1. a, ramus descendens hypoglossi; b, N. hypoglossus; c, ramus tho- 
racoabdominalis vagi; d, ramus cervicalis vagi. Osmic acid. X 36. 
Fig. 4 Section of the vagus at the level indicated by 4, figure 1. a, ramus 
descendens hypoglossi; 6, N. hypoglossus; c, ramus thoracoabdominalis vagi; d, 
ramus cervicalis vagi. Osmiec acid. X 36. 
hypoglossi is composed almost exclusively of large myelinated 
fibers, while in the hypoglossal there are a few medium and 
small sized ones. There also are two or three clumps of closely 
packed unmyelinated fibers. These resemble the bundles of 
sympathetic fibers in the mammalian hypoglossal (Koch, un- 
published observations) and are here interpreted as such. 
Above this level the vagus and accessory nerves have fused 
into a single trunk and lost their separate identity. The vago- 
accessory trunk has now divided into two well defined fascicles 
separated by a sharp line but not by any connective tissue 
septum. The lightly stained bundle (c in fig. 3) is the tho- 
racoabdominal ramus of the vagus and all its fibers are destined 
for the thorax and abdomen. The other, more darkly stained, 
fascicle (d, fig. 3) is the cervical ramus of the vagus, and all its 
fibers end in structures in the neck. These fascicles differ 
