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LATERAL MUSCLES OF NECK 231 



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 suc- 

 ceeding fleshy portion, in passing along the neck, receives 

 fasciculi from each of the cervical vertebrae except the first 

 two. The dorsal division of the muscle is inserted into the 

 mastoid process by a flat tendon which fuses with that of the 

 splenius; the ventral division is inserted into the wing of the 

 atlas by a ribbon-like tendon in common with the splenius and 

 mastoido-humeralis. 



Relations. — Superficially, the splenius muscle and dorsal 

 branches of the cervical nerves; deeply, the complexus, the 

 spinalis colli, and the oblique muscles of the head. The superior 

 cervical vessels cross the deep face of the muscle obliquely at 

 the level of the sixth and seventh cervical vertebra'. 



Blood-supply. — Vertebral and superior cervical arteries. 



Nerve-supply.— Dorsal branches of the last six cervical 

 nerves. 



6. Complexus (M. semispinalis capitis). — This is a 

 large triangular muscle which lies chiefly on the ligamentum 

 nuchse, under cover of the splenius and trachelo-mastoideus 

 muscles. 



Origin. — (1) The second, third, and fourth thoracic spines, 

 in common with the splenius and serratus anticus; (2) the 

 transverse processes of the first six or seven thoracic vertebrae; 

 (3) the articular processes of the cervical vertebrae. 



Insertion. — The posterior surface of the occipital bone, 

 external to the funicular portion of the ligamentum nuchae. 



Action. — It is the chief extensor of the head and neck. Act- 

 ing singly, the muscle inclines the head to the same side. 



Structure. — The origin of the muscle at the withers is apo- 

 neurotic. In the neck the bundles arising from the articular 

 processes run obliquely upward and forward, giving the lower 

 I I 3 3 1^ part of the muscle a distinct pennate character. The upper 

 part of the belly is crossed obliquely' by four or five tendinous 

 o I '\ intersections. The insertion is by a strong tendon. 

 E I I Relations. — Superficially, the rhomboideus, serratus magnus, 



splenius, and trachelo-mastoideus muscles; deeply, the liga- 

 mentum nuchae, the multifidus cervicis, longissimus, and the 

 oblique and posterior straight muscles of the head, the deep 

 or superior cervical vessels, and the dorsal cutaneous branches 

 of the cervical nerves. 



Blood-supply. — Deep cervical, vertebral, and occipital 

 arteries. 



Nerve-supply. — Dorsal branches of the last six cervical 

 nerves. 



7. Multifidus cervicis (M. semispinalis colli; transverse 

 spinous muscle of neck). — This muscle lies on the arches of the 



H.v^'i ^ "^"-g last five cervical vertebrae. It consists of five or six segments. 

 ^ s § 1 :3 5 Origin. — The articular processes of the last five (or four) 



s 1^ S » £ cervical and the first thoracic vertebrae. 



"o ^- ;.- J S Insertion. — The spinous processes of the cervical vertebrae. 



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