306 S. WALTER RANSON 
sheath; but the sympathetic trunk and _ thoracoabdominal 
vagus run together into the thoracoabdominal cavity. Opposite 
one of the lowest cervical vertebrae and under cover of the 
plastron the sympathetic leaves the vagus and turns abruptly 
dorsad toward the inferior cervical ganglion of the sympathetic. 
At the point at which the two nerves separate there is developed 
on the one the middle cervical sympathetic ganglion, and on 
the other the ganglion thoracoabdominale vagi (fig. 2). 
A short distance below the thoracic ganglion the recurrent 
nerve is given off and, running under the arch of the aorta, 
turns back along the trachea. <A little farther caudad the nerve 
breaks up into pulmonary, cardiac and gastric rami. 
While the arrangement of the ganglia and branches of the 
vagus given above may be taken as typical, there is a very wide 
range of variation in individual specimens; especially important 
variations occur in the position of the cervical ganglion of the 
vagus which is often located higher up on the nerve before it 
has divided instead of on the cervieal ramus. However, as 
~ three specimens were found in which the ganglion was located 
on, and restricted to, the cervical ramus it is safe to say that 
in the other cases in which it was located on the undivided trunk 
the ganglion really belonged to the cervical division of the nerve. 
STRUCTURE OF THE VAGUS AND ITS GANGLIA 
1. Roots. The rootlets of the vagus are all alike in their 
structure, differing in this respect from those of the dog (Chase 
and Ranson). The vagus rootlets of the turtle are composed 
of myelinated fibers of all sizes, small and medium sized ones 
predominating. Among the myelinated are large numbers of 
unmyelinated fibers. The spinal root of the accessory is 
formed of medium and large sized myelinated fibers. The 
bulbar roots of the accessory are formed of myelinated fibers 
of all sizes, the small ones greatly predominating. There are 
very few unmyelinated fibers in the rootlets of the accessory 
nerve. 
2. The vagus nerve in the neck. As will be seen by figure 1, 
the vagus, accessory and hypoglossal nerves form a single nerve 
