402 
MR. W. K. PARKER OK THE SKELETON 
olfactory nerves and cribriform plate. If we now compare tlie diagram (Plate 17, 
fig. 4), and the meagre description just given of the cranial nerves of this great 
Myxinoid, we shall find many things become clear that have been for a long time 
confusing to the students of these types ; for there has, apparently, been much con¬ 
crescence and much suppression in the development of the cranial nerves in these 
remarkable Fishes. In the Lamprey, also, there are some very abnormal characters. 
The right determination of the skeletal parts is largely dependent upon a true 
knowledge of the cranial nerves, and, vice-versd, they have to be considered in their 
relation to the supporting skeleton. 
Muller II. (“ Gehororgans,” plate 3, figs. 3, 4, 5) gives upper, lower, and side 
figures of the brain of Petromyzon fluviatilis, and he enumerates the following nerves 
going off from it right and left, viz. : I. Olfactory (large and single) ; II. Optic 
(moderate size); III. Oculo-motor (very small) ; IV. Trochlearis (still smaller); V. 
Trigeminus ; VI. Facialis; VII. Acusticus ; VIII. Vagus ; IX. Hypoglossus. 
In the second plate figures are given of the brain of Bdellostoma (figs. 8, 9) and 
Myxine (figs. 11, 12). 
In these closely related types we have the following cranial nerves given by 
Muller, viz. 
I. Olfactory (in fire main nerves on each side, and these also each breaking into a 
small pencil of branches) ; II. Optic (very small in Bdellostoma, but paired; much 
smaller and only drawn on the right side in Myxine); III. Trigeminus (very large); 
IV. Facialis; V. Acusticus; and VI. Vagus (very large). 
In his paper (III.) on the ‘ Neurologie ’ of the Myxinoids, Muller (plate 2, figs. 
4, 5) gives the cranium and its nerves in Bdellostoma from above and below. In the 
upper view the optic nerve is shown passing under the ophthalmic nerve, which is 
drawn with its first bifurcation. The larger part of the nerve is seen penetrating the 
suborbital fenestra, and in the lower view this lower part (3rd branch) is seen broken 
up into four branches, the second of 'which is re-split. But in the upper view there is 
also, behind the ophthalmic (1st branch), a small nerve passing over the palato- 
quadrate cartilage ; this he does not name. 
But in the next plate (III., figs. 2 and 3) we have this 2nd branch of the 
trigeminal figured on both sides. In the upper view (fig. 3) it is seen as passing over 
the cartilage bounding the suborbital fenestra, and in the side view (fig. 2) it is 
shown as running forwards along the upper surface of the palato-quadrate nearly up 
to the beginning of the soft “ pre-palatine horn.” Here it is called “ Vorderen ober 
Ast des Trigeminus,” whilst the large branches that grow from the stalk that pierced 
the fenestra are called “Unter Aeste desselben,”—the 1 ewer branches of the same 
nerve. In the upper view (fig. 3), where the 1st and 2nd branches (only) are drawn, 
he calls this small nerve “Hinterer oberer Hautast des Trigeminus;” whilst the 
branches of the great 1st division (Ophthalmic), “ Vorderer ober Ast des Trigeminus,” 
he calls “ 1, Hautast; 2, Nasenast; 3, Oberer Endast; and 4, Unterer Endast.” 
