PREVERTEBRAL MUSCLES 355 



Variations. — The scaleni present numerous variations in the extent of the costal and ver- 

 tebral attachments. The degree of fusion of the various fasciculi likewise varies so much that 

 different authors have described varying numbers of muscles into which the scalenus mass 

 should be subdivided. A muscle frequently present is the scalenus minimus. This arises 

 from the anterior tubercle of the sixth or sixth and seventh cervical vertebrae, and is inserted 

 into the first rib behind the sulcus for the subclavian artery. It sends a process (Sibson's 

 fascia) to the pleural cupola and serves to make the pleura tense. Zuckerkandl found it in 

 22 out of 60 bodies on both sides; 12 times on the right side only, 9 times on the left. It is 

 innervated by the eighth cervical nerve. When absent, a ligamentous band takes its place. 

 An intertransversariiis lateralis longus, may extend from the posterior tubercles of the 3-5 

 transverse processes to the tip of the seventh transverse process and divide the muscle fasciculi 

 near their origin into dorsal and ventral divisions. 



8. THE PREVERTEBRAL MUSCULATURE 

 (Fig. 352) 



This deep-seated musculature extends along the ventro-lateral surfaces of the 

 three upper thoracic and the cervical vertebrae to the skull. It is composed of 

 two muscles. The longus colli arises from the bodies of the three thoracic and 

 from the bodies and transverse processes of the third to the sixth cervical verte- 

 brae, and is inserted into transverse processes and bodies of the cervical vertebrae. 

 The longus capitis (rectus capitis anterior major) arises from the transverse 

 processes of the fourth, fifth, and sixth cervical vertebrae, and is inserted into the 

 basilar process of the occipital bone. These muscles flex, abduct, and rotate 

 the head and neck. All of them are supplied by direct branches from the anterior 

 divisions of the cervical nerves. They are probably specialised from the ventro- 

 lateral portions of the cervical myotomes. Similar muscles are found in all 

 vertebrates with well-developed necks. The rectus capitis anterior (minor) 

 represents an anterior cervical intertransverse muscle. 



FASCIA 



(Figs. 351, 357) 



The muscles are firmly bound to the vertebral column by the prevertebral fascia described 

 in connection with the scalene muscles and by the septa which extend in between the muscles 

 of this group and between them and the scalenus anterior. 



MUSCLES 



(Fig. 352) 



The longus colli. — This muscle may be compared to a triangle, the base of which extends 

 from the anterior tubercle of the atlas to the body of the third thoracic vertebra and the apex 

 of which is the transverse process of the fifth cervical vertebra. The complex construction of 

 the muscle makes it advisable to consider it as divided into three parts. 



The supero-lateral portion consists of fasciculi which arise from the anterior tubercles of 

 the transverse processes of the third, fourth, fifth, and sixth cervical vertebraj and from the body 

 of the third thoracic and become fused into a belly which is inserted into the anterior tubercle 

 of the atlas. 



The median portion is formed of muscle fasciculi which arise from the antero-lateral parts 

 of the bodies of the first three thoracic vertebrae and the last three cervical vertebrae by tendin- 

 ous processes. These fascicuh fuse into a belly which terminates by three flat tendinous fas- 

 cicuh on the antero-lateral surfaces of the bodies of the second, third, and fourth cervical 

 vertebrae. 



The infero -lateral portion is applied to the inferior lateral surface of the median portion. 

 It arises from the lateral parts of the bodies of the first three thoracic vertebrae and is inserted 

 by tendinous processes into the transverse processes of the fifth and sixth cervical vertebrae. 



Nerve-supply. — By branches from the second to sixth cervical nerves which send rami 

 to the various constituent fasciculi of the muscle. 



The longus capitis (rectus capitis anterior major). — Origin. — By cylindrical tendons from 

 the tips of the anterior tubercles of the third, fourth fifth, and sixth cervical vertebrae. The 

 tendons send up aponeurotic expansions on the outside of the fasciculi, which arise from them. 

 These fasciculi fuse into a dense muscular belly to which is usually added a fasciculus from the 

 longus colli. The insertion takes place into the impression on the inferior surface of the basilar 

 portion of the occipital bone, extending lateral to the pharyngeal tubercle outward and for- 

 ward. The insertion of the fibre-bundles from the third vertebra is direct; the other fibre- 

 bundles are inserted largely into a tendinous lamina which covers the middle of the ventral 

 surface of the muscle and from which, in turn, other fibre-bundles arise. It is an incomplete 

 digastric muscle. Nerve-supply. — The first, second, third, and fourth cervical nerves send 

 branches into the ventral surface of the muscle. 



