56 Proceedings of Royal Society of Edinburgh. [sess. 
the vagus of Chimoera would be in the unique condition of consist- 
ing of five perfectly distinct nerves. As far as I am aware, this 
condition is most nearly approached in Torpedo , the IXth and Xth 
cranial nerves of which I dissected some time ago at Professor 
Ewart’s suggestion. In Chimoera the vagus arises by five main roots, 
of which the most anterior is the root of the lateralis. The next 
three roots are those of the three branchial nerves which supply 
the posterior demi-branch (or third) on the first branchial arch, two 
demi-branchs on both the second and third arches, and a single 
demi-branch on the anterior face of the last or fourth branchial arch. 
There are thus five gills, of which the first and last (on the hyoid 
and fourth branchial arches) consist of a single demi-branch only, 
and the remaining three of two demi-branchs each. The distribu- 
tion of each branchial nerve to a great extent resembles that of the 
IXth, and will be described in my next paper. The posterior root 
of the Xth is that of the intestinal. This nerve forms an elaborate 
plexus on the stomach and oesophagus, and the only nerve from the 
vagus to the heart which I have yet found, is a very fine branch of 
the intestinal which ran in the wall of the sinus venosus. In 
several Elasmobranchs I have found a nerve from the last 
branchial division of the vagus going to the heart, but have 
hitherto not seen any traces of it in Chimoera. The lateralis, besides 
innervating the lateralis canal, gives off a nerve dorsally to the 
commissural and median canal (shown by oblique shading — L). 
This dorsal branch requires very careful dissection, as it would be 
very easy to mistake its origin, as, indeed, I did mistake it myself 
until a careful revision showed me my error. Further complications 
in dissecting the vagus are the dorsal branches from the anterior 
spinal nerves passing through the cranium, which seem to arise from 
the IXth and Xth. I shall describe these nerves fully and the 
other spinal nerves in my future paper. 
Conclusion . — The study of the cranial nerves of Chimoera un- 
doubtedly emphasises the affinities which the Holocephali have 
with the Elasmobranchs, and more particularly with the sharks, 
but it may be added with equal certainty that both as regards the 
anatomy of the brain and the distribution of the cranial nerves, 
the Holocephali are more archaic and have not undergone such 
differentiation as the Elasmobranchs evidently have. 
