84 JoURNAL OF CoMPARATIVE NEUROLOGY. 
peripheral end-organs with the dorsal cornu of the cord through 
the medium of the dorsal root. These two divisions of a spinal 
nerve comprise the principal number of fibres in the two roots. 
(c) Viscero-motor; these fibres take their origin from a group of 
cells, the paracentral nucleus of Onur and Co ttins (’98), lying 
lateral to the canalis centralis; they emerge through both the 
ventral and the dorsal roots, and are distributed to the non- 
striated muscles of the viscera. (ad) Viscero-sensory neurones, 
from the viscera, through the dorsal root, to termination in the 
intermediate zone of the gray matter. 
A new era in the investigation of cranial nerves was inau- 
gurated by Srronec (’95) when he made the application of these 
principles to larval amphibians. Srrone found that it is prac- 
ticable to recognize certain distinct classes of fibres or compo- 
nents of the cranial nerves, which are to be distinguished from 
each other by their size and histological characters, by their 
_ central origin or connections, and by their ultimate distribution. 
KinGspury (’97) made a careful extension of these findings to 
several ganoids and teleosts ; while HERRICK (97, ’98, ’99) has 
traced the conditions in the bony fish, Menidia, with admirable 
clearness. Certain conclusions reached by JonnsTon (’98b) from 
his study of the ganoid brain stand apart from the general 
trend of recent work, and to these we shall return further on. 
The principles developed by the researches of STRONG, 
Kinespury, and HERRICK, may now be applied to the cranial 
nerves of Mustelus. There are to be distinguished five systems 
of nerve components : 
a. The Somatic Motor System.—This system of neurones 
is homologous with the ventral-cornu neurones of the spinal 
cord. The fibres take origin from cells having a ventral loca- 
tion in the brain, and they innervate striated somatic muscles. 
The only representatives of this class are the nerves of the eye- 
muscles, the III, IV, and VI, respectively. 
b. The General Cutaneous System is socalled because con- 
cerned with the innervation of the skin of the head, but it is 
not associated with specialized peripheral sense-organs of any 
kind. Its fibres are components of the V, IX, and X nerves, 
