MOTOR NUCLEI IN PHYLOGENY 483 
viscero-motor column in Bdellostoma should not, for the same 
reason, be more extensive than the vagus nucleus in Petromyzon 
also. 
Attention has already been drawn by R6thig and Kappers to 
the apparent ‘telescoping’ of the brain in Myxine and to the 
seeming crowding of the vagus rootlets by the otic capsule as a 
result of such a process (88). Evidences of a similar extensive 
‘telescoping’ in the medulla are not lacking in Bdellostoma. It 
would appear that the motor and sensory nuclei of the spino- 
occipital nerves have migrated rostrad, while the superficial 
attachments of their respective roots have suffered but little 
disturbance. In other words, the spinal cord appears to be 
impacted, as it were, into the medulla. 
The peripheral area innervated by the spino-occipital nerves 
is directly contiguous to that supplied by the trigeminus. Their 
rostral position places the sensory spino-occipital nuclei more 
directly in connection with the great general cutaneous area of 
the medulla. 
This rostral situation has thus given rise to a close associa- 
tion of the general cutaneous centers of medulla and cord in 
Bdellostoma, similar in all essentials to that brought about in 
higher forms by a greater development and specialization of the 
tractus spinalis nervi trigemini. <A different method has been 
used in the two cases to attain the same result, viz., the close 
association of centers whose peripheral areas are subject to the 
influence of simultaneous stimulation. 
The rostral projection of the spmo-occipital nuclei in front 
of the exit level of the first spino-occipital nerve appears to be 
less extensive in Myxine than in Bdellostoma, though it is a 
curious fact that the distance between the rostral extremity of 
the nucleus in question and the level of the facial nerve, is ap- 
proximately equal in the two forms (fig. 7). 
In Bdellostoma, on account of the larger size of the vagus 
column, this nucleus overlaps the spino-occipital nucleus, as 
already described. However, but little evidence can be adduced 
to indicate any caudal displacement of the vagus column, the 
distance between the caudal end of this nucleus and the first 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 27, NO. 4 
