522 DAVIDSON BLACK 
relations obtaining in the oculomotor and trochlear nuclei. The 
rostral position of the motor VII nucleus, together with the 
caudal extent of the motor V nucleus, point to the probability 
that these characters are dependent upon the development of a 
modified type of opercular respiration and the consequent more 
close association of the motor nuclei upon whose coordinate 
action certain respiratory movements depend. 
Finally, it would appear that further evidence for the grouping 
of modern ganoids together and apart from teleosts is furnished 
by the close correspondence of the motor nuclear pattern in all 
ganoids examined and by the characteristic differences of this 
pattern on the one hand from that of sharks and on the other 
from that of teleosts. 
TELEOSTEI 
Motor nucler in Ameiurus nebulosus and Solea vulgaris 
Among teleosts, two forms whose life habits present a very 
marked contrast, have been selected for study: the flat-fish Solea 
vulgaris and the siluroid Ameiurus nebulosus. 
Occipito-spinal nuclei and roots (Nu. et rad. mot Nn. occ. spin.). 
In Solea and also in Ameiurus the rostral end of the somatic 
motor column of the cord is continued for some distance unin- 
terruptedly into the medulla, and there forms the nucleus of 
origin of certain precervical motor rootlets. 
The general term ‘spino-occipital’ has been made use of in 
describing this region in selachians and ganoids to distinguish 
the rostral portion of the somatic motor column of the trunk and 
its associated motor rootlets. Since the reduction of the spino- 
occipital elements among teleosts is evidently more extensive 
than is the case in lower forms (e.g., selachians and ganoids) as 
well as in many higher forms (e.g., amphibians), it seems desira- 
ble to indicate this fact by the use of some term other than 
spino-occipital in describing this region in teleosts, especially as 
the arrangement of the elements in the rostral end of the somatic 
motor column among Teleostei presents certain characteristics 
distinctive of the group. For this reason in the present de- 
