18 H. BERKELBACH VAN DER SPRENKEL 
myelin sheaths do not descend, but ascend, obliquely and, run- 
ning in a fronto-dorsal direction, join the dorsal endings of the 
IX, as already stated above. The other somewhat thicker and 
more heavily myelinated visceral sensory fibers also ascend for 
a short distance, turn again mesad over the spinal V tract, and 
then end, descending near the lateral wall of the ventricle. 
Although these fibers descend for a short distance, the visceral 
sensory root of the vagus does not form a real tractus solitarius, 
as occurs in reptiles, birds and mammals. 
The positions of the different constituents of the visceral 
sensory X roots are such that the better myelinated fibers (the 
mesial root) lie ventro-medial to the poorly myelinated dorsal 
root fibers. They do not leave the brain directly, but run along 
the lateral border inside the brain for some distance and join 
other vagus fibers. The different constituents of these roots 
ean still be distinguished after the roots have left the brain. 
The same process is repeated in the successive caudal roots, 
and also the position of the poorly myelinated dorsal fibers— 
’ lateral from the better myelinated mesial fibers—is repeated in 
the posterior levels of the bulb. 
More caudally the poorly myelinated fibers not only leave the 
gray substance by curving dorsally around the lobus X, but they 
also leave it directly. This process is followed (perhaps it is the 
consequence of it) by a course of the poorly myelinated fibers 
through the spinal V tract instead of dorsally of it. 
Concerning the somatic sensory fibers of the second vagal 
root, it may be mentioned that they form a dorsal part of the 
sensory root near its entrance. When entering the brain they 
are at first still separated from the descending V by the visceral 
sensory fibers; but as soon as these disappear from the sections 
they closely join the descending V, with which they can be traced 
to the posterior horn of the cervical cord. 
It is known that in Petromyzon (Johnston"*) and in primitive 
sharks (Kappers!’) somatic sensory fibers occur in the VII and 
16 Johnston, The nerve components of Petromyzonts. Morph. Jahrb., Bd. 34, 
1905. The nervous system of vertebrates. Philadelphia, 1906, p. 107 and fig. 50, 
17 Kappers, Der Geschmack, perifer und central. Psychiatrische en Neuro- 
logische Bladen, Nos. 1 and 2, 1914, fig. 3, pp. 102 and 103. 
