512 The American Naturalist. [June, 
micus profundus originates in more posterior segments, has re- 
placed the lost sensory elements of the original nerve of the 
third or mandibular segment. 
The Vllth nerve is a splanchnic efferent nerve consisting 
of both large and small fibres, the small fibres passing into the 
geniculate ganglion, which would therefore be the ganglion of 
the anterior root. As to the somatic efferent fibres, Gaskell 
has not been able as yet to find these. In this nerve, too, the 
degenerate remains of the sensory fibres and ganglion are 
The Vlllth nerve is dismissed from consideration, since it 
is a nerve of special sense, and this might possibly justify its 
claim to an independent position. Summing up, then, we 
find that " in the group of motor cranial nerves, formed by the 
Illd, IVth, Vlth and motor part of the Vth, and Vllth nerves, 
we have at least four fully formed segmental nerves which for 
some reason or other have lost a certain portion of their origi- 
nal components." 
"In the group of nerves which arise from the medulla ob- 
longata we find all the components which make up a fully 
formed spinal nerve, or rather group of nerves; here, how- 
ever, there is no sign of any degeneration of any special 
group of fibres, but rather a dislocation and scattering of the 
different components, so that the cranial nerves of this group 
form parts of a number of segmental nerves instead of each 
one forming a single nerve." Both the IXth and Xth are 
purely splanchnic nerves. Each possesses two ganglia : the 
ganglion jugulare and ganglion petrosum on the one hand, and 
the ganglion jugulare ^r\d gayiglion trunci vagi on the other. 
Gaskell considers that the two jugular ganglia represent the 
stationary afferent ganglia of the IXth and Xth nerves, while 
the ganglion petrosum glossopharyngei and Xht ganglion trunct 
vagi represent the vagrant efferent ganglia. The spinal acces- 
sory consists of large and small fibres. The large ones arise 
in all the roots of the nerve, the small fibres are confined to 
the medullary and upper cervical roots, and pass into the 
ganglion trunci vagi. All the fibres are splanchic efferent 
fibres. The hypoglossus is a purely somatic motor nerve. It 
represents the separated somatic efferent fibres of this region. 
The origin of the fibres of the cranial nerves as well as the 
structure and function of their peripheral nerve fibres, goes to 
prove the spinal nature of the cranial nerves, for the groups of 
cells, which give origin to the cranial nerves, are the direct 
