4 LO ie 
THE CERVICAL PLEXUS. 577 
The clavicular branches (rr. supra-claviculares) pass over the middle third of the 
clavicle, beneath the platysma, and can be traced as low as the nipple. The 
acromial branches (rr. supra-acromiales) pass over or through the insertion of the 
trapezius muscle, and over the outer third of the clavicle, to the shoulder, where 
they supply the skin as far down as the lower third of the deltoid muscle. 
Deep Branches.—The deep branches of the cervical plexus are naturally 
separated into an external and an internal set by their relation to the sterno-mastoid 
Great occipital 
nerve 
y : 
/] 
N \ \\ Ss HA, { B , aN — . b ~- 
- \ = f ‘ Nerve to 
} \ . : mylohyoid 
Y) \ \ . \ . iylohyo 
\ \\ \ \ <a 
Small occipital = | 
OLY Ose comciata. ihc Nt i] 
\\ Wf) 
Great auricular ll, 
10(=)\'A=; Sn DL pe a \ 7) 
Nerves to levator eer Sh a i) Wf 
—__ WH 
anguli scapulee— ———____ 
~ arfiels 7 tala -_— 
Superficial cervical fl! Hy poglossal 
nerve | nerve 
i Internal laryn- 
y geal nerve 
=a ~_ Nerve to 
Spinal accessory —————_—_——____ a) / 
Nerve to trapezius — sae Rs is ; ly 
ae W er thyrohyoid 
Acromial ) branches ( - } 
from 
| cervical | it 
Sternal) plexus 
Descendens 
; hypoglossi 
Clavicular ; ee 
Posterior scapular 
nerve 
Posterior thoracic 
nerve — 
Fic. 427.—THrE TRIANGLES OF THE NECK (Nerves). 
muscle. Beneath the muscle, the external branches are directed outwards towards 
the posterior triangle, the internal branches inwards towards the anterior triangle. 
The external branches consist of muscular and communicating nerves, which 
for the most part occupy the posterior triangle. 
The muscular branches are the following: (1) To the sterno-mastoid, from the 
second cervical nerve. This enters the muscle on its deep surface and communicates 
with the spinal accessory nerve. (2) To the trapezius, from the third and fourth 
cervical nerves. These nerves cross the posterior triangle and end in the trapezius, 
after having communicated with the spinal accessory nerve, in the posterior triangle, 
and beneath the muscle. (3) To the levator anguli scapula, from the third and 
fourth cervical nerves. Two independent branches enter the outer surface of the 
muscle in the posterior triangle. (4) To the scaleni (medius and posticus), from 
the third and fourth cervical nerves. 
The communicating branches, already mentioned, are three in number. They 
37 
