594 
the separation which takes place in the fat cells 
between the solid and the fluid elements of fat. 
As the combination of the primitive muscular 
fibres, ina common sheath, forms the muscle, 
so the union of the primitive nervous fibres, in 
a similar way, forms the nerve. And as the 
primitive fibre of muscle passes undivided from 
one point of the muscle to another, so the nerve 
tube exhibits no subdivision in its course. 
Branching of nerves.—The main trunk of a 
nerve breaks up into its component bundles, as 
it passes from centre to periphery, yielding up 
branches to the various parts it is destined to 
connect with the nervous centre. These branches 
generally come off at acute angles, and soon 
plunge into the muscles and other parts to which 
they tend, dividing and subdividing as they pro- 
ceed. Such is the most common mode of sub- 
division, but there are many exceptions: some- 
times a branch separates from the parent trunk at 
an acute angle, and then turns to run in an op- 
posite direction, forming an arch, from the con- 
vexity of which several branches are given off. 
Such a nerve is said to be recurrent; the in- 
ferior laryngeal nerve takes this course. The 
anastomotic arches between the emerging spinal 
nerves, round the vertebral laminz, are also 
exceptions to the separation at acute angles. 
Before a branch separates, it often happens 
that the parent trunk presents an enlargement 
for some distance above the point of visible 
separation. This is due to the fact that the fibres 
which compose the future branch begin to 
loosen their connection with the trunk for some 
way before they actually leave it; and the con- 
necting areolar membrane becomes conse- 
uently looser.and more abundant. Hence 
the trunk of the nerve appears enlarged, with- 
out any increase in the number of its nervous 
elements. This may be well seen in the auri- 
cular nerve of the neck, as it winds upwards 
over the sterno-mastoid muscle. 
Anastomosis of nerves—In their branchings 
nerves subdivide, not only to pass immediately 
to their muscles or other distant parts, but 
also to connect themselves by certain of their 
filaments with other nerves, and to follow 
the course of the latter, whether onward or re- 
trograde, peripherad or centrad, instead of ad- 
hering completely to that of the primary trunk. 
By these means, nervous filaments connected 
with very different parts of the brain and spinal 
cord become bound together in the same fasci- 
culus, and a nerve is formed compounded of 
tubes possessing very opposite functions. The 
anastomosis of nerves thus formed differs very 
obviously from the more correctly named anas- 
tomosis of bloodvessels, for in the latter case the 
canals of the anastomosing vessels are made to 
communicate and their contents are mingled; 
but in the former the nerve filaments are simply 
placed in oe apni There is no fusion 
of the one into the other, no admixture of the 
pulpy contents of the nerve-tubes, which con- 
tinue their course as perfectly insulated as if 
we were placed singly and had no connexion 
with others. 
The simplest kind of anastomosis is that 
which occurs in the formation of almost every 
NERVOUS SYSTEM. (Nerve.) 
down the limb: those filaments which 
spinal nerve. The anterior and the posterior — 
roots of these nerves, emerging from different 
of the spinal cord, and possessing, as 
is now proved, very different functions, are — 
united after passing through the dura mater 
and bound together as one nerve; the com 
ponent tubules being so completely intermixec 
that the future ramifications of the nerve ma 
enjoy the double function derived from the 
diverse endowment of the originally compo- 
nent tubules. al 
And even in a nervous trunk thus forme 
there occurs a remarkable interchange of place 
between the component filaments, which are 
thereby made to decussate each other within the 
trunk of the nerve (fig. 332). Bichat s: 
amused myself one day in attentively following 
all the filaments of the sciatic nerve some distance 
Diagram to show the decussation of the primitive j , 
within the trunk of a nerve. (After Valentin, ) 
the exterior of the trunk above, I fou 
greatest part, forming its centre 
Kronenberg states that in some nerves the 
communications are so frequent that one cann 
follow a single fascicle for any distance; wh 
in other nerves, as the external cutaneous ner 
of the arm, he found — bundles wh 
passed through a distance of upwards ¢ 
inches without uniting with eighboast z OF 
This is an anatomical fact of no mean imp 
tance, as applicable to the explanation of mat 
apparently anomalous symptoms in neu 
and other nervous affections. 4 
A second form of anastomosis may be 
explained by referring to that with which 
who have made the superficial dissection © 
neck must be familiar,—namely, the ang 
mosis of the descending branch of th 
with the cervical plexus. Certain fibres, ¥ 
pass from the medulla oblongata as part 
ninth nerve, leave that nerve as it cros 
carotid artery, pass down in front of the‘ 
and apply themselves to a descending brat 
the cervical plexus, forming in front of thi 
tid artery and jugular vein an arch with the 
cavity directed upwards, several nerves p 
from the convexity to neighbouring mu 
A little careful dissection shows that se 
the nervous filaments which are given 0 
the convexity are derived from the ninth 
and others from the descending branch of 
cervical plexus ; whilst others seem to fo1 
complete arch and to be equally connected w 
both nerves. If we trace them from the) 
nerve, we find them passing upwards at 
wards into the descending branch of t 
* Anat. Générale, t. i. p. 128, ed. Il a 1. 
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