6388 ANIMAL PHYSIOLOGY. 
Does the above-mentioned plan of distribution, etc., hold 
for the cranial nerves ? 
Leaving out the nerves of special sense (olfactory, optic, 
and auditory), the other cranial nerves may be thus divided: 
1. A foremost group of nerves, wholly efferent in man, viz., 
the third, fourth, motor division of the fifth, the sixth, and 
seventh. 2. A hindmost group of nerves of mixed character, 
viz., the ninth, tenth, eleventh, and twelfth. 
The nerves of the first group, since they have both large- 
fibered, non-ganglionated motor nerves, and also small-fibered 
splanchnic efferent nerves, with vagrant ganglia (ganglion 
oculomotorii, ganglion geniculatum, etc.), resemble a spinal 
nerve in respect to their anterior roots. They also resemble 
spinal nerves as to their posterior roots, for at their exit from 
the brain they pass a ganglion corresponding to the stationary 
posterior ganglion of the posterior root of a spinal nerve. 
These being, however, neither in roots nor ganglion functional, 
are to be regarded as the phylogenetically (ancestrally) degen- 
erated remnants of what were once functional ganglia and 
nerve-fibers ; in other words, the afferent roots of these nerves 
and their ganglia have degenerated. 
The hindmost group of cranial nerves also answers to the 
spinal nerves. They arise from nuclei of origin in the medulla 
and in the cervical region of the spinal cord, directly continu- 
ous with corresponding groups of nerve-cells in other parts of 
the spinal cord; but in these nerves there is a scattering of the 
components of the corresponding spinal nerves. Certain pecul- 
iarities of these cranial nerves seem to become clearer if it be 
assumed that, in the development of the vertebrate, degenera- 
tion of some region once functional has occurred, in conse- 
quence of which certain portions of nerves, etc., have disap- 
peared or become functionless. 
It is also to be remembered that a double segmentation 
exists in the body, viz., a somatic, represented by vertebre and 
their related muscles, and a splanchnic represented by visceral 
and branchial clefts, and that these two have not followed the 
same lines of development; so that in comparing spinal nerves 
arranged in regard to somatic segments with cranial nerves, 
the relations of the latter to the somatic muscles of the head 
must be considered; in other words, like must be compared 
with like. 
