MOTOR NUCLEI IN PHYLOGENY Zt 
One of the most characteristic features of this avian nuclear 
pattern lies in the association of the V-VII motor nuclei and the 
situation of the facial motor nuclei on, or more frequently rostral 
. to the exit level of their motor root. It has been pointed out 
above that a similar association of V-VII motor nuclei is not 
found as a group character elsewhere in the vertebrate phylum 
except in cyclostomes. The association of facial and trigeminal 
motor nuclei in birds would seem to be due largely to the domi- 
nant influence of sensory trigeminal impulses upon the reflex 
action of both facial and trigeminal musculature in those forms. 
The mutual association of the V-VII motor nuclei in close con- 
tiguity with the chief sensory center acting reflexly upon them 
thus affords a striking illustration of Kappers’ neurobiotactic 
concept. 
An association of the motor glossopharyngeal and dorsal motor 
vagal nuclei, such as characterizes birds, is encountered as a 
group feature elsewhere among vertebrates only in petromy- 
zonts.'6 In birds, though the IX—X musculature has completely 
lost its primitive respiratory function, yet the effectors concerned 
act synergically and coordinately in all movements of the fore- 
gut and are dominated reflexly by visceral sensory impulses 
entering by way of the afferent IX and’ X roots. Thus these 
motor nuclei also are associated in the neighborhood of the chief 
center acting reflexly upon them. 
The intermedius X—XII motor complex constitutes a third 
characteristic feature of the nuclear pattern within the brain 
stem of birds, and one apparently unique among vertebrates. 
It has been shown to be highly probable that this peculiar com- 
plex was evolved as a consequence of the development of the 
laryngo-syringeal mechanism peculiar to birds. Its possession 
by certain forms, such, for example, as Struthio, Ciconia, and 
Casuaris, in which intrinsic syringeal musculature is lacking, 
constitutes strong evidence in favor of considering the-relatively 
simple syringeal organization of these animals to be due to a 
16 Among teleosts, although a similar nuclear association has been observed 
sporadically in various forms (e.g., Ameiurus, 8), in no case does this character 
constitute a group feature. 
