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LATERAL CERVICAL MUSCLES 271 
jor, obliquus capitis posterior, complexus, longissimus capitis et atlantis, splenius, 
scalenus, and longissimus dorsi et costarum muscles; deeply, the vertebrae, the 
longus colli muscle, and the vertebral vessels. The muscles are perforated by 
branches of these vessels and by the primary branches of the cervical nerves. 
Blood-supply.—Vertebral artery. 
Nerve-supply.—The cervical nerves. 
LATERAL CERVICAL MUSCLES 
This group consists of twelve pairs of muscles arranged in layers. 
First LAYER 
1. Trapezius cervicalis.—Described on p. 293. 
Sreconp LAYER 
2. Rhomboideus cervicalis.—Described on p. 293. 
3. Serratus cervicis.—Described on p. 297. 
Tuirp LAYER 
4. Splenius.—This is an extensive, flat, triangular muscle, partly covered by 
the preceding three muscles. 
Origin.—The second, third, and fourth thoracic spines by means of the dorso- 
scapular ligament and the funicular part of the ligamentum nuche. 
Insertion.—The nuchal crest, the mastoid process, the wing of the atlas, 
and the transverse processes of the third, fourth, and fifth cervical vertebre. 
Action.—Acting together, to elevate the head and neck; acting singly, to in- 
cline the head and neck to the side of the muscle acting. 
Structure—The muscle arises in the withers from the anterior part of the 
dorso-scapular ligament, which also affords attachment to the rhomboideus, ser- 
ratus dorsalis, and complexus muscles. The fibers pass upward and forward 
toward the head and the first cervical vertebra. The insertion on the occipital 
bone and the mastoid process is by means of a thin aponeurosis common to the 
brachiocephalicus and longissimus capitis. The atlantal insertion is by a strong, 
flat tendon, in common with the longissimus atlantis and the brachiocephalicus. 
The remaining insertions are fleshy digitations. 
Relations.—Superficially, the skin and fascia, the trapezius, rhomboideus 
cervicalis, serratus ventralis, and posterior auricular muscles: deeply the com- 
plexus and longissimus dorsi muscles. 
Blood-supply.—Deep cervical and dorsal arteries. 
Nerve-supply.—Dorsal branches of the last six cervical nerves. 
Fourta LAYER 
5. Longissimus capitis et atlantis..—This muscle consists of two parallel, fusi- 
form portions. It lies between the deep face of the splenius and the ventral part 
of the complexus. 
Origin.—(1) The transverse processes of the first two thoracic vertebre; (2) 
the articular processes of the cervical vertebree. 
Insertion.—(1) The mastoid process; (2) the wing of the atlas. 
Action.—Acting together, to extend the head and neck; acting singly, to flex 
_ the head and neck laterally or to rotate the atlas. 
Structure—The origin from the thoracic vertebre is by aponeurotic slips 
which blend with the complexus. The succeeding fleshy part, in passing along 
1Also termed the trachelo-mastoideus. 
