540 DAVIDSON BLACK 
dorsal and ventral roots are regularly represented. In Pleuro- 
nectidae the dorsal root of nerve b may be missing and both the 
dorsal and. ventral roots of nerve ¢ are fused with nerve b as 
they make their exit from the skull but the arrangement of the 
nerves from this point caudad is similar to that obtaining among 
siluroids. 
The peripheral relations of the cervical nerves in Ameiurus 
appear to conform closely with Furbringer’s generalized scheme 
for the family outlined above. Thus, according to Wright 
(1. ¢.), the first spinal nerve (occipito-spinal b) possesses both 
dorsal and ventral roots, which unite however, and emerge by a 
common foramen through the exoccipital bone (auximetameric 
cranium). ‘The second spinal nerve of this author (Furbringer’s 
nerve 4) is separated from the first by a considerable distance— 
more than twice the distance intervenes between the exit levels 
_of these two nerves than between those of the second and third. 
This apparent hiatus in the series would seem to indicate the 
disappearance of the nerve c. The dorsal and ventral roots of 
the second nerve emerge through separate dural foramina, as do 
those of the third nerve, but owing to the modification of the 
anterior vertebrae in connection with the auditory organ, they 
pass directly through the membranous wall of the neural canal. 
The dorsal and ventral roots of the fourth and following cervical 
nerves emerge through separate foramina in the arches of the 
corresponding vertebrae. 
Within the central nervous system also there are many evi- 
dences that both reduction and rostral displacement have 
occurred in the precervical somatic motor column in Ameiurus 
as compared with more primitive forms. As these characteris- 
tics are typical of all teleosts to a greater or less extent, a gen- 
eral summary of the evidences furnished by the group as a 
whole will be of value in the present connection. 
Tvidences of reduction. 1) With the exception of Hippo- 
glossus, in all teleosts examined the distance between the exit 
level of the first precervical motor root and that of the motor 
glossopharyngeus is greater than in selachians. 2) Except in the 
Pleuronectidae, the distance between the exit level of the first 
