62 OSBORN. (Voi. II. 
Proteus presents the widest departure from the common type, 
inasmuch as the Trigeminus and upper root of the Facial are 
given off very close together, and, so far as observed, but two 
branches spring from the Gasserian ganglion. The oth and roth 
pairs arise some distance behind and are followed by the 12th, 
which springs from two small roots and has the same position as 
the succeeding nerve, as an anterior spinal nerve root (Fig. 3). 
THE MEDULLA OBLONGATA OF CRYPTOBRANCHUS. 
General Structure. I have not made a close examination of 
the entire section of the medulla at different levels, having 
devoted most attention to the lateral regions, which are espe- 
cially connected with the tracts and nuclei of the cranial nerves. 
As we would naturally anticipate, in an animal of such low 
organization as Cryptobranchus, the transition from the spinal 
cord to the medulla is a gradual one, but it by no means follows 
that we can readily homologize the medulla and spinal cord 
sections. 
As we ascend from the level of the roth pair (Fig. 10), at 
which the general arrangement of the gray and white matter of 
the cord is fully preserved, we find the tracts and nuclei of the 
posterior nerves, and the deep ascending tracts, which are at the 
extreme lateral limits of the medulla, are gradually thrust down- 
wards by the nuclei and tracts of the more anterior nerves. 
Thus the nuclei of one pair of nerves are overlapped from above, 
and then replaced by the nuclei of the pair in front of them, 
and so on. This superposition of the posterior by the anterior 
nuclei is exclusively in the lateral portions of the medulla, and 
none of the nerves between the 12th and 6th pairs 
arise from the region corresponding to the an- 
terior horn of the gray matter of the cord, 
The central region of the medulla is in general composed of 
five main areas. 1. At the floor of the ventricle on each side is a 
mass of sensory cells. 2. Below these, scattered along the whole 
medulla, are multipolar ganglion cells, which are especially 
large and numerous opposite the exit of the Acusticus. 3. On 
either side of the sulcus are the large fibres of the posterior 
longitudinal fasciculus, and below these are the Miillerian fibres. 
4. Below this, in the median line, are decussating fibres and the 
1Nucleus centralis, Stieda. 
