LATERAL MUSCLES OF NECK 229 



Action. — To bend the neck laterally. 



Structure. — They contain strong tendinous intersections. 



Relations. — Superficially, the mastoido-humeralis, rectus capitis anterior major, 

 complexus, trachelo-niastoideus, splenius, scalenus, and longissimus muscles; 

 deeply, the vertebra?, 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. — \'ertebral artery. 



Nerve-supply. — The cervical nerves. 



LATERAL MUSCLES 

 This group consists of twelve pairs of muscles arranged in layers. 



First Layer 



1. Trapezius cervicalis. — Described on p. 250. 



Second Layer 



2. Rhomboideus cervicalis. — Described on p. 25L 



3. Serratus magnus (AL serratus cervicis). — Described with the thoracic part 

 on p. 254. 



Third Layer 



4. Splenius. — This is an extensive, flat, triangular muscle, partly covered by 

 the precechng three muscles. 



Origin. — The second, third, and fourth thoracic spines by means of the dorso- 

 scapular ligament, and the funicular portion of the ligamentum nuchse. 



Insertion. — The occipital crest, the mastoid process, the wing of the atlas, 

 and the transverse processes of the third, fourth, and fifth cervical vertebrae. 



Action. — Acting together, to elevate the head and neck; acting singly, to 

 incline 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, 

 serratus anticus, 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 

 splenius, trachelo-mastoideus, and mastoido-humeralis. The atlantal insertion 

 is by a strong, flat tendon, also in common with these muscles. The reinaining 

 insertions are fleshy digitations. 



Relations. — Superficially, the skin and fascia, the trapezius rhomboideus, 

 cervicalis, serratus magnus, and posterior auricular muscles; deeply, the com- 

 plexus, trachelo-mastoideus, and longissimus muscles. 



Blood-supply. — Deep cervical and dorsal arteries. 



Nerve-supply.— Dorssd branches of the last six cervical nerves. 



Fourth Layer 



5. Trachelo-mastoideus (M. longissimus capitis et atlantis). — This muscle 

 consists of two parallel, fusiform 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 vertebrae; (2) 

 the articular processes of the cervical vertebrae. 



Insertion. — (1) The mastoid process; (2) the wing of the atlas. 



