LATERAL CEBVICAL MUSCLES 271 



jor, obliquus capitis posterior, complexus, longissimus capitis et atlantis, splenius, 

 scalenus, and longissimus dorsi et costarum muscles; deeply, the vertebrae, the 

 longus coin 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. 



Second Layer 



2. Rhomboideus cervicalis. — Described on p. 293. 



3. Serratus cervicis. — Described on p. 297. 



Third 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 nucLse. 



Insertion. — The nuchal 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 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 

 splenius and longissimus capitis et atlantis. The atlantal insertion is by a strong, 

 flat tendon, also in common with these muscles and the brachiocephalicus. The 

 remaining insertions are fleshy digitations. 



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

 cervicalis, serratus ventrahs, 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. 



Fourth 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 vertebrae; (2) 

 the articular processes of the cervical vertebrae. 



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 vertebrae is by aponeurotic slips 

 which blend with the complexus. The succeeding fleshy part, in passing along 



'Also termed the traohelo-mastoideus. 



