SUPERFICIAL CERVICAL REGION. 333 



of the neck, into a thick rounded muscle, which is inserted, by a strong tendon, 

 into the outer surface of the mastoid process, from its apex to its superior bor- 

 der, and by a thin aponeurosis into the outer two-thirds of the superior curved 

 line of the occipital bone. The Sterno-mastoid varies much in its extent of 



Fig. 220. Muscles of the Neck, and Boundaries of the Triangles. 



attachment to the clavicle : in one case the clavicular may be as narrow as the 

 sternal portion ; in another, as much as the three inches in breadth. When 

 the clavicular origin is broad, it is occasionally subdivided into numerous slips, 

 separated by narrow intervals. More rarely, the corresponding margins of the 

 Sterno-mastoid and Trapezius have been found in contact. In the application 

 of a ligature to the third part of the subclavian artery, it will be necessary, 

 where the muscles come close together, to divide a portion of one or of both. 



This muscle divides the quadrilateral space at the side of the neck into two 

 triangles, an anterior and a posterior. The boundaries of the anterior triangle 

 are in front, the median line of the neck ; above, the lower border of the body 

 of the jaw, and an imaginary line drawn from the angle of the jaw to the 

 mastoid process ; behind, the anterior border of the Sterno-mastoid muscle. 

 The boundaries of the posterior triangle are, in front, the posterior border of the 

 Sterno-mastoid ; below, the upper border of the clavicle ; behind, the anterior 

 margin of the Trapezius. 1 



The anterior edge of the muscle forms a very prominent ridge beneath the 

 skin, which it is important to notice, as it forms a guide to the surgeon in 

 making the necessary incisions for ligature of the common carotid artery, and 

 for ossophagotomy. 



Relations. By its superficial surface, with the integument and Platysma, from 



1 The anatomy of these triangles will be more exactly described with that of the vessels of the 

 neck. 



