ROOTS, TRUNK, BRANCHES OF VAGUS NERVE 51 



in the neck as a rounded fascicle, separated from the vagus by a 

 connective tissue septum but contained with the vagus in a com- 

 mon connective tissue sheath. Even when flattened out on the 

 vagus the s^onpathetic is usually separated from the vagus by a 

 thin connective tissue septum. Holzmann and Dogiel (10) 

 found that in some dogs the sympathetic trunk was easily dis- 

 sected from the vagus. These must have been cases in which it 

 remained as a separate rounded fascicle. 



Following the sympathetic trunk upward in the neck we find 

 that it parts company with the vagus at a variable distance 

 below the nodose ganglion, and runs as a separate trunk to the 

 superior cervical gangUon. Just below this ganglion it con- 

 tains both fine medullated and non-medullated fibers. The fine 

 medullated fibers are ascending pre-ganglionic fibers from the 

 thoracic spinal nerves and are very numerous. As the sympa- 

 thetic trunk is traced into the ganglion the medullated fibers are 

 lost among the ganglion cells. 



The presence of large numbers of non-medullated fibers in the 

 vagus of the dog suggests the possibility of an admixture of sym- 

 pathetic fibers because of the close relation of these two nerves 

 in that animal. This raises the question as to whether the ob- 

 servations here recorded are applicable to the human vagus which 

 is not included in a conmion connective tissue sheath with the 

 sympathetic trunk. A short stretch of the human vagus just 

 below the nodose ganglion was removed within a few hours after 

 death and stained by the pyridine-silver method. This presents 

 essentially the same picture as the cervical vagus in the dog. 

 The chief difference being that the non-medullated fibers are 

 more evenly distributed throughout the nerve in the dog. In 

 the human vagus they tend to form larger bundles and there are 

 some bundles of medullated fibers quite free from them. But so 

 far as one can tell, the relative proportion of the two kinds of 

 fibers is about the same in the dog and in man. 



Several sets of serial sections were gone over carefully to de- 

 termine to what extent sympathetic fibers enter into the com- 

 position of the vagus in the dog. The two trunks, although 



