280 ME. J. L. CLAEKE OUST THE INTIMATE STEUCTUEE OE THE BEAM. 
(22) But besides this most intimate and important connexion between the two nuclei 
— the hypoglossal and the spinal-accessory — through the medium of their cells r the 
spinal-accessory nerve , as I formerly showed on several occasions, has a separate origin 
from the hypoglossal nucleus ; and I also showed that both the vagus and glossophar 
ryngeal nerves have each a separate origin from the same source. These interesting 
facts have been fully confirmed by Dr. John Dean, of Boston, U. S. *. In birds this 
separate origin of the vagus nerve from the hypoglossal nucleus is so striking, that in 
well-made preparations it may be seen almost at a glance f. In fishes I have recently 
discovered a beautiful and peculiarly interesting illustration of the same anatomical fact. 
In these animals there is no separate hypoglossal nerve, but the tongue is supplied by a 
branch of the vagus. Now I was very desirous of knowing what was the nature of the 
vagal nucleus in these animals, and of ascertaining whether it was a double or com- 
pound nucleus consisting of the vagal and hypoglossal nuclei joined together. On 
examination I found that the lower division of the vagus nerve, after proceeding trans- 
versely through the lateral part of the medulla, bifurcates into two distinct roots of con- 
siderable size; and that while one of these curves backward to spread into the grey 
substance behind the canal, the other bends forward into a round or oval nucleus, which, 
in regard both to the character of its cells and its position in front and at the side of 
the canal, corresponds exactly to the hypoglossal nucleus of the higher vertebrata. 
These appearances are so well marked, — this anterior nucleus is so distinct, and its 
connexion with the corresponding root of the vagus nerve is so evident, — that in well- 
made preparations they may be seen with the greatest facility. In fishes the roots of 
the vagus external to the medulla consist of two sets, — the one a little above the other. 
The lower set are on a level with the calamus scriptorius ; the upper set are on a level 
with the large vagal eminence of grey substance which rests on the floor of the fourth 
ventricle beneath the cerebellum. Fig. 33, Plate XI. represents a transverse section of 
the medulla oblongata of the Cod at the point of the calamus scriptorius, just where 
the canal (6) opens into the fourth ventricle, and therefore on a level with the lower set of 
vagal nerves (14). The anterior portion of the medulla, 1, 1, 2, 3 (see left side of figure), 
on either side, consists of some nerve-cells, and a network of fibres and blood-vessels 
containing in its meshes a multitude of longitudinal bundles of different sizes. Many 
of these bundles are exceedingly large, particularly along the inner side next the raphe, 
— as represented by the round or oval spaces (1,1), — and in front at 2, where they appear 
to correspond to the anterior pyramids of the higher vertebrata. The nerve-cells are 
of considerable size, and chiefly collected into a small group (3) .near the centre. 
Behind the two lateral halves of this anterior portion of the medulla, and lodged in a 
depression between them, are two other larger longitudinal bundles of fibres (4) ; and 
immediately behind these are two oval and still larger longitudinal columns of nerve- 
cells (5), which have precisely the same position at the side, and in front, of the canal 
* On the Grey Substance of the Medulla Oblongata and Trapezium. By John Deast, M.D., 1864, pages 
27 28. 
t See my Memoir on the Medulla Oblorgata, Philosophical Transactions, 1858, Plate XIII. fig. 18. 
