The Cranial Nerve Components of Petromyzon. 191 
cutaneous and speeial eutaneous components. The second is the visceral 
group, including visceral motor, general visceral and special visceral 
(gustatory) components. The somatie group supplies all ceutaneous 
and somatie motor innervation which in the trunk region, is supplied 
by the ventral rami of the spinal nerves, and the fibers to the neu- 
romasts in addition. The visceral group corresponds to the vagus 
trunk of opereulated animals, where the general eutaneous compo- 
nents of the vagus form only dorsal (oceipital) rami and the vagus 
trank propor is only branchial and intestinal. In selachians it is 
probable that an intermediate condition will be found where the 
general eutaneous component is distributed to the skin of the bran- 
chial segments by way of the branchial nerves very much as in 
Petromyzon. 
Visceral Motor System. 
With regard to tbe visceral motor components Petromyzon pre- 
sents no peculiarities except those which have been discussed in 
connection with the eye-musle nerves. The presence of visceral 
components, either motor or sensory, in the spinal nerves has not 
been investigated. This would scarcely be possible except by means 
of GOLGI preparations. 
Segmental Relations of the Cranial Nerves. 
The segmentation of the head has been discussed from the stand- 
point of the theory of nerve components in a recent communication 
(23). The fuller knowledge of the cranial nerves of Petromyzon 
necessitates no change in the eonelusions there arrived at, but rather 
brings new facts to their support. T’'he adult arrangement as well 
as the embryology of the pre-auditory neuromast nerves and ganglia 
is eonsistent with the view that they belong to segments anterior to 
the acusticus segment. The presence of a general eutaneous com- 
ponent in the VII! nerve fills out the complete series of general 
cutaneous nerves, one for each segment beginning with the N. pro- 
fundus. The relations of the mandibular and hyomandibular nerves, 
as the nerves of the mandibular and hyoid segments, leaves no 
ground for the supposition that a branchial segment has been lost 
in this region (v. WısHE, Miss PLATT, NEAL). 
It is in the postauditory region that the results in Petromyzon 
are most important for segmentation. The following review of the 
eonditions in this region will show that there are a larger number 
