574 THE NERVOUS SYSTEM. 
primary division of a spinal nerve (Fig. 421, p. 567). 
Space; near its origin it possesses gray and white 
courses through the interval between the 
branches to these 
rami 
It occupies an intercostal 
communicantes ; it 
intercostal muscles; it supplies 
muscles and gives off, when it reaches the side of the 
chest, a lateral branch, which, piercing the external intercostal muscle, is distri- 
1S-O; 
LAr 
Fic. 425.—THE CrervicaL PLExus. 
Internal branches 
Communicating to 
Superficial Division. 
Ascending branches (Ase,)— 
8.0. Small occipital. Hy. Hypoglossal, 
G.A. Great auricular. Va. Vagus, 
S.C. Superficial cervical. Sy. Sympathetic ganglion. 
D.Cery, Descendens cervicis. 
Descending (supra-clavicular) branches 
(Desc. )— Musecular— 
Acr. Acromial. M! Rectus capitis anticus minor, 
Cl. Clavicular. and lateralis. 
St. Sternal. M?, Longus colli, and rectus 
ee capitis anticus major, 
Deep Division, Sc.A.  Scalenus anticus. 
External branches— Phr. Phrenic nerve. 
Communicating (C.) to spinal acces- G.Hy. Nerve to genio-hyoid. 
sory nerve (Sp. Acc.), Th.Hy. Nerve to thyro-hyoid. 
Muscular— D.Hy. Descendens hypoglossi, 
S.M. Sterno-mastoid. Ansa. Ansa hypoglossi. 
Abr Trapezius. S.Th. Nerve to sterno-thyroid. 
L.A.S. Levator anguli scapule, S.Hy. Nerve to sterno-hyoid. 
Se.M. Scalenus medius. O.Hy. Nerves to omo-hyoid. 
in front. The lateral and anterior branches 
buted to an area of 
skin over the lateral 
part of the trunk, 
contiguous with a 
sinilar area behind, 
innervated by the 
cutaneous branches 
of the posterior 
primary division of 
the same nerve. 
The lateral branch 
generally subdivides 
into a smaller os- 
terior and a larger 
anterior trunk, as it 
pierces the muscles 
clothing the wall of 
the chest. The an- 
terior primary divi- 
sion of the nerve 
then pursues its 
course obliquely for- 
wards to the side of 
the sternum, where, 
after piercing the 
pectoral muscles, it 
appears superficially 
as the anterior ter- 
minal cutaneous 
branch. This sup- 
ples an area of skin 
continuous with that 
supplied by the 
anterior part of the 
lateral branch of the 
Same nerve. Such 
a nerve thus sup- 
plies, by means of 
its lateral and 
anterior branches,an 
area of skin which 
(with the area sup- 
plied by the cuta- 
neous branch of its 
posterior — primary 
division) forms a 
continuous and un- 
interrupted belt, 
extending from the 
middle line behind 
to the middle line 
of the nerve innervate in their 
course the intercostal and other muscles, to be afterwards mentioned in detail. 
