658 
trunk and the extremities. Of these branches 
the anterior one is generally much the larger. 
An exception, however, to this arrangement 
occurs in the case of the first nog nerve (the 
tenth pair of Willis), to which Winslow gave the 
appropriate name sub-occipital nerve, to indicate 
its peculiarity of character. This nerve some- 
times has only one root, and that corresponds to 
the anterior. More generally it has two roots, 
of which, unlike the other spinal nerves, the 
anterior is the larger, containing, according 
to Asch, from three to five or seven bun- 
dies of filaments, whilst the posterior contains 
two or three, or at most four much smaller 
bundles. Very frequently the posterior fila- 
ments of either the right or left side unite with 
the spinal accessory, a slight enlargement or 
knot being formed at the point of junction ; 
from this place a bundle of filaments emerges 
equal in size to the posterior root, and takes 
the ordinary course of that root, a small gan- 
glion being formed upon it at the usual situa- 
tion. Frequently, however, this ganglion is 
wanting. The compound nerve formed from 
the junction of these two roots, besides giving 
off communicating filaments to the sympathetic, 
divides as the other spinal nerves do into an 
anterior and posterior root, of which, however, 
contrary to the usual arrangement, the posterior 
is the larger. , 
The spinal nerves are arranged naturally into 
classes according to the regions of the spine in 
which they take their rise. We number eight 
in the cervical region, the sub-occipital in- 
cluded ; twelve in the dorsal region ; five in 
the Inmbar, and six in the sacral regions. All 
the nerves, after the second, pass obliquely 
outwards and downwards from their emer- 
gence from the spinal cord to their exit from 
the vertebral canal, and this obliquity gradu- 
ally increases from the higher to the lowest 
nerves. The roots of the nerves possess cer- 
tain characters, of which some are common to 
all, and others are peculiar to the nerves of 
particular regions. ‘ 
All the spinal nerves arise from the cord by 
separate fasciculi of filaments, which, as they 
approach the dura mater, converge to each 
other and are united together to constitute the 
anterior or the posterior roots. The posterior 
roots of opposite sides lie at a pretty uniform 
interval, from the upper to the lower part of 
the cord, indicating but a very trifling change 
in the thickness of the posterior columns 
throughout their entire course. The ganglia 
on the posterior roots are all proportionate to 
the size of their respective roots. 
The characters proper to the nerves of parti- 
cular regions may be stated as follows :*— 
The cervical nerves exhibit much less obli- 
quity of their roots than the other vertebral 
nerves. The second cervical nerve is trans- 
verse (the first passing a little upwards as well 
as outwards); the succeeding nerves slope 
downwards and outwards, the lowest being 
* In the succeeding statements I have followed 
Cruveilhier’s description, which I have verified, 
excepting in a few points which are specified. 
NERVOUS SYSTEM. (Nervous Cextres. Tur Sprnat Corp.) 
the most oblique; the obliquity, he 
never exceeds the depth of a single verte 
The roots of the nerves in the cervical re 
gion are of considerable size. The pe 
roots bear a larger proportion to the ¢ 
than in any other part of the spine. Accor 
ing to Cruveilhier, the ratio is as 3 to 1, am 
this estimate is probably correct. It applie 
not only to the entire root, but to the fascieu 
of filaments which enter into their formation. 
The nerves in this region increase rapid! 
from the first to the fifth, and then maintai 
nearly the same size to the eighth. — 
The dorsal nerves, with the exception of 
first, which closely resembles a cervical nerv 
have very peculiar characters, . 
There is a manifest increase in the obliquit 
of the roots, so that the length of each rot 
within the spinal canal equals the height of ; 
least two vertebra. And it may be remark 
that the apparent obliquity is less than the rea 
for each root remains in contact with the co 
for a short distance after its actual emerge 
from the substance of it, so that the po 
separation is some way below the point ¢ 
emergence. 
The interval between the roots is greater 
the dorsal region than any other segment: 
the cord. The bundles, which compose t 
roots, are smaller than elsewhere. “4 
We observe a very slight disproportion 
tween the anterior and posterior roots in 
dorsal region. The latter, however, still 
tain predominance of size. 
Lumbar region—From the dorsal regic 
its terminal extremity the surface of the sp 
cord is covered both on its err ind | 
rior aspects by the fasciculi of origin 
Peiaber geil sacral nerves. They emerg 
close to each other upon those surfaces, 
the intervals between the sets of fase 
proper to each root are extremely short 
that they form an uninterrupted series of 
dles on each surface. a. 
The proportion of the posterior to the 
rior roots in the lumbar region is as 2 to” 
cording to Cruveilhier, or as 14 to 1, W 
seems to me to be nearer the trath 
there does not —_ to be any materia 
ference in point of size between the pos 
and anterior fascicles.* 
A very interesting feature in the origin 
lumbar and sacral nerves may be seen | 
serving the relation to each other of tl 
rior and posterior roots of opposite si 
the vanpelaive surfaces of the ‘could T 
terior roots of opposite sides may be Ss 
approximate the median line gradually a 
descend, until at the lowest points they 
touch. On the contrary, the posteri 
continue nearly in the same sequence 
way down. It may, therefore, be sup 
that in the tapering of the cord the ar 
eos, 
“2 
. 
? 
* M. Blaudin assigns the following proj 
of the posterior to the anterior roots in the 
regions ; in the cervical region as 2 = 15 
dorsal region as 1 : 1; and in the lumbar ant 
regions as 1}: 1. ‘ 
