EXAMINATION OF SOME SPINAL NERVES 63 
and the mid-ventral lines, differs curiously in these respects from the skin-fields delimited for all 
other cranio-spinal nerves. The area lies on the opening of the ist visceral cleft. It is overlapped 
by the fields of the Vth cranial and of the Ilnd and IlIrd cervical nerves. The auricular branch 
of the vagus is, by some authorities, considered the ramus lateralis of the vagus of lower vertebrates ; 
its skin-field points, however, rather to its being a branchial branch. Its fibres, traceable by 
dissection to the ganglion of the root of the vagus, may or may not actually arise in that ganglion. 
In my experiments, the roots of tlie vagus have not been cut, for the reasons stated above. This 
skin-field offers the instance, unique in my experience, of a root distribution over an area 
absolutely isolated from the median lines of the body. It is the only true exception to the zonal 
type of distribution. It indicates in the strongest way a very great difJerence between the vagus 
Fig. 3 
Combined posterior bor- Dotted line marks boun- Completely delimited 
der of Vth cranial and dary of auricular of area of auricular of 
auricular of vagus (?). vagus (?). vagus (r). 
Broken line marks ant. 
edge of Ilird cervical. 
and the ordinary spinal nerves. I cannot help regarding it as evidence that the vagus is a visceral 
nerve, and supplies the visceral depth of the 2nd visceral cleft, just as the diagram, p. 55 supra, of 
the tongue and fauces shows the glosso-phar)'ngeal nerve supplying the depth of tlie ist visceral 
cleft. That the field of the vagus comes so far toward the mouth of the cleft as to reacli external 
auditory meatus is not extraordinary, when it is remembered how widely the posterior root-nerves 
overrun the limits of the segmental borders of their metamers. 
XIIth Cranial Nerve 
It was long since pointed out by Mayer, Luschka, Vulpian and others, that in various 
Mammals, including Man, the hypoglossal nerve occasionally possesses a dorsal root, and that this 
root possesses a ganglion. In the artiodactylous Ruminants, and to a less degree in Carnivora, this 
dorsal ganglionated root is regularly present,* altliough in the latter always small. Embryological 
study of the Mammalia reveals the fact that the XIIth cranial nerve throughout the class is 
originally a group of true spinal nerves, and that the dorsal roots of these, each provided with 
* A. Froi iep ami W. Beck, ' Anat. Anzeig.,' vol. lo, p. 688, 1895. 
