THE CERVICAL PLEXUS. 57 
Or 
CERVICAL NERVES. 
The anterior primary divisions of the cervical nerves, together with parts of the 
_ first and second thoracic nerves, are distributed to the head, neck, and upper 
| extremity. The first four dervical nerves, by means of the cervical plexus, innervate 
the neck; the last four cervical nerves, together with a large part of the first 
thoracic nerve, through the brachial plexus “supply the upper limb. The second 
thoracic nerve may contribute a trunk to this plexus, and always assists in the 
innervation of the upper limb. 
THE CERVICAL PLEXUS 
The anterior primary divisions of the first four cervical nerves are concerned 
in forming the cervical plexus. Each nerve emerges from the spinal canal behind 
the vertebral artery. Hach is joied on its emergence from the intervertebral 
foramen, at the side of the spine, by a gray ramus communicans from the superior 
cervical ‘ganglion of the sympathetic. In the neck the nerves are concealed by 
the sternomastoid muscle; in front lies the rectus capitis anticus major, and 
behind are the scalenus medius, and (behind the first or suboccipital nerve) the 
rectus capitis lateralis. The cervical plexus is constituted by the combination 
of these nerves in an irregular series of loops under cover of the sterno-mastoid 
muscle. 
From these loops the branches of distribution arise, as (#) cutaneous branches to 
the head, neck, and shoulder; (4) muscular branches to the muscles of the neck; 
and (¢) communicating branches to the vagus, spinal accessory, hypoglossal and 
sympathetic nerves. 
For convenience of description, the nerves derived from the plexus may be 
classified as follows :— 
I. Superficial (cutaneous) Branches— 
A. Ascending Branches (C. 2 and 3). b. Descending (supraclavicular) Branches 
Small occipital, (C. 3 and 4)— 
Great auricular, Acromial, 
Superficial cervical. Clavicular, 
Sternal. 
Il. Deep (muscular and communicating) Branches— 
A. External Branches. B. Internal Branches. 
1. Muscular branches to 1. Muscular branches to 
Sternomastoid (C. 2), Prevertebral muscles (C. 1, 2, 
Trapezius (C. 3, 4), 3, 4), 
Levator anguli scapulee (C. 3, Infrahyoid muscles (C. 1, 2, 
4), 3) (ansa hypoglossi), 
Scaleni (medius and posticus, Diaphragm (C. 3, 4) (phrenic 
(C. 3, 4). nerve). 
2. Communicating branches to 2. Communicating ae to 
Spinal accessory nerve (C. 2, Vagus nerve CG 512) 
3, 4). Hypoglossal nerve e (C. tl -2))s 
C. Hypoglossi (C. 2, 3), 
Sympathetic (C. 1, 2, 3, 4). 
The second, third, and fourth cervical nerves are the chief nerves engaged in 
forming the plexus, The first cervical nerve only enters into the formation of a 
small part—the internal portion of the deep part of the plexus. 
Superficial Cutaneous Branches.—These nerves, six in number, are entirely 
cutaneous. They radiate from the cervical plexus, and appear in the posterior 
triangle of the neck at the posterior border of the sterno-mastoid muscle. 
The small occipital nerve (n. occipitalis minor) is variable in size and is some- 
times double. Its origin is from the second and third cervical nerves (more rarely 
