[Fig. 158].—Superficial Nerves of the Neck.

M. clavotrapezius has been partly removed. 1, N. accessorius; 2-4, ventral rami of second to fourth cervical nerves; 5, N. auricularis magnus; 6, N. cutaneus colli. a, M. clavotrapezius (cut); b, M. splenius; c, M. levator scapulæ ventralis; d, M. cleidomastoideus; e, M. sternomastoideus; f, parotid gland.

Dorsal Rami (Rami posteriores).—The dorsal ramus of the first nerve (N. suboccipitalis) supplies the short dorsal muscles which move the head and connect the atlas and skull. In the second nerve the dorsal ramus is much larger, forming N. occipitalis major. It sends small branches to the muscles about its origin, then turns craniad on the surface of the obliquus superior muscle, passes through the biventer cervicis and splenius, joins a small branch from the third nerve, and reaches the dorsal surface of the back of the head. It passes craniad, lying beneath the levator auris longus, emerges from between the two divisions of this muscle, and supplies the skin and cutaneous muscles between the two external ears. The dorsal rami of the other cervical nerves supply muscles and integument on the back of the neck.

Ventral Rami (rami anteriores).—These pass ventrad between the transverse processes of the vertebræ, except in the case of the first nerve ([Fig. 156], j). This passes ventrad from the atlantal foramen along the groove for the vertebral artery, through the notch in the wing of the atlas, and across the lateral surface of the longus capitis muscle (5). Here it sends a branch caudad to join the second cervical (k), then crosses the vagus (d′) and sympathetic and the carotid artery, giving off communicating branches to the vagus and sympathetic, and uniting with a branch of the descending ramus of the hypoglossal (f). At the lateral surface of the larynx it turns caudad, following the lateral border of the sternothyroid muscle (7), and is distributed to the sternohyoid (8) and sternothyroid (7).

The ventral ramus of the second nerve ([Fig. 158], 2) receives a branch from that of the first nerve, passes laterad between the levator scapulæ ventralis (c) and the cleidomastoid (d), receives a communicating branch from the third cervical (3), sends a branch to N. accessorius (1) and numerous small nerves into the sternomastoid (e) and cleidomastoid (d), then turns craniad and divides into N. auricularis magnus (5) and N. cutaneus colli (6).

N. auricularis magnus (5), the great auricular nerve, passes dorsocraniad across the lateral surface of the sternomastoid (e) to the lateral and caudal surface of the external ear and parotid gland (f), where it ramifies. The cutaneus colli (6) is the smaller, ventral, division of the second nerve; it may receive also an accession from the third. It passes to the integument over the ventral part of M. masseter and ventrad of that muscle.

The third nerve ([Fig. 158], 3) communicates with the second and supplies the levator scapulæ ventralis (c), cleidomastoid (d), sternomastoid (e), longus capitis, and other muscles of this region and aids in forming the cutaneus colli (6). The fourth (4) and fifth are distributed to the muscles and integument of the sides of the neck. A branch of the fourth supplies the integument in the hollow of the shoulder, and one from the fifth follows the vena cephalica and supplies the integument over the shoulder. The fifth by sending a branch to aid in forming the phrenic nerve ([Fig. 157], f) may be considered to enter partly into the brachial plexus.

Owing to the intercommunicating branches between the ventral roots of the first five cervical nerves, these are sometimes considered as forming a loose plexus which receives the name cervical plexus.

The sixth, seventh, and eighth cervical nerves (with a part of the fifth) become interconnected with each other and with the first thoracic to form the brachial plexus.

The Brachial Plexus