AN EXPERLMENTAL STUDY OF THE VAGUS 

 NERVE 



MARTIN R. CHASE 

 From the Anatomical Laboratory of the Northwestern University Medical School^ 



FOUR FIGURES 



In a previous paper a study was made of the structure of the 

 roots, trunk and branches of the vagus nerve (Chase and Ran- 

 son '14). 



It was shown, in conformity with the work of Molhant ('10) 

 and Van Gehuchten and Molhant ('11) that the vagus nerve in 

 the dog contains myelinated fibers which can be classified as 

 large, medium and small. In addition there were found enor- 

 mous, numbers of unmyelinated fibers. These are present in 

 certain of the vagus rootlets, and throughout the tmnk of the 

 vagus. In the cervical and thoracic tiimk they constantly 

 increase in proportion to the myelinated fibers, so that at the 

 level of the diaphragm the vagus is almost a pure unmyelinated 

 nerve. 



The most of the large myelinated fibers, and many of medium 

 size, are given off in the cervical branches of the vagu-. The 

 bronchial and esophageal rami receive nearly all of the remain- 

 ing myelinated fibers. Relatively few unmyelinated fibers are 

 found in the cervical branches. The increased proportion of 

 unmyelinated fibers in the lower vagus is due in part at least 

 to the withdrawal from the trunk of the myelinated fibers by 

 the upper branches. Essentially the same histological picture 

 was seen in sections from the vagus of man (Ranson '14), the 

 rat and the rabbit. 



Gaskell '86 observed unmyelinated fibers in the vagus nerve, 

 and found the lower thoracic vagus to contain few myelinated 

 fibers. He interpreted the unmyeUnated fibers in the vagus 



1 Contribution No. 37. 



421 



