242 HEAD AND NECK 



of the thorax (p. 341). In the neck the nerve runs down- 

 wards and anteriorly, on the superficial surface of the scalenus 

 anterior, which forms its deep relation. In this part of its 

 course it is covered by skin, superficial fascia and platysma, 

 deep fascia and stern o-mastoid; and, deep to the sterno-mastoid, 

 it is overlapped by the internal jugular vein, and it is crossed 

 by the omo-hyoid, the anterior jugular vein, and the transverse 

 cervical and transverse scapular arteries on both sides ; on the 

 left side by the thoracic duct, and on the right side by the 

 right lymph duct. At the root of the neck it passes from the 

 medial border of the anterior scalene to the anterior surface 

 of the first part of the subclavian artery ; and it is covered 

 anteriorly by the clavicle on both sides, by the subclavian 

 vein on the right side, and by the commencement of the in- 

 nominate vein on the left side, and it crosses either anterior 

 or posterior to the internal mammary artery. It gives off no 

 branches in the neck, but it sometimes receives a communica- 

 tion from the nerve to the subclavius. 



After the dissector has completed the examination of the formation, the 

 relations, and the branches of the cervical plexus, he should replace the 

 divided infra-hyoid muscles in position and study their attachments and 

 relations. 



The Infra-hyoid Muscles are a series of flat, band-like 

 muscles which lie upon the trachea, thyreoid gland, and 

 larynx. They are disposed in two strata viz., the omo-hyoid 

 and the sterno-hyoid constituting a superficial layer ; and 

 the sterno-thyreoid and thyreo-hyoid a deep layer. 



Musculus Omohyoideus. This is a two-bellied muscle. The 

 posterior belly springs from the upper border of the scapula 

 and the upper transverse scapular ligament. It crosses the 

 posterior triangle of the neck, dividing it into occipital 

 and subclavian portions, and terminates under cover of the 

 sterno-mastoid muscle in an intermediate tendon ; and it is 

 superficial to the phrenic nerve and the scalenus anterior. 

 The tendon is held in position by a strong process of cervical 

 fascia which is firmly attached below to the sternum and the 

 first costal cartilage. The anterior belly emerges from under 

 cover of the anterior border of the sterno-mastoid, and takes 

 an almost vertical course through the anterior triangle. It is 

 inserted into the lower border of the body of the hyoid bone, 

 at the lateral side of the sterno-hyoid. In the anterior 

 triangle of the neck it forms the boundary between the 



