Sterno-inastoid ; Wry -neck 3 



Acting with its fellow, it draws back and fixes the head and neck, 

 and raises, or depresses, and fixes the shoulders. Its nerve-supply is 

 from the spinal accessory, and also from the anterior divisions of the 

 third and fourth cervical nerves. Either with or without the sterno- 

 mastoid, the trapezius is apt to cause spasmodic wry-neck. 



The Hgamentum nuchce ascends from the seventh cervical spine 

 to the external occipital protuberance, and gives attachment to fasciae 

 and muscles. 



The sterno-cleido-mastoid is attached, as its name suggests, to 

 the sternum, clavicle (xXets-, ^XftSos-, clavis\ and mastcid process. The 

 sternal origin is by a tendon from the front of the manubnum ; and the 

 clavicular origin is by a wide mass of muscle and tendon from the upper 

 border of the inner end of that bone. The two heads are separated 

 by a narrow triangular interval, which corresponds with the common 

 carotid artery, the vagus, and the last part of the internal jugular. 



The muscle is enclosed in a definite sheath of the deep cervical 

 fascia. 



The two heads of origin slope upwards and backwards, and, having 

 blended a little below the middle of the neck, are inserted into the 

 mastoid process and into the superior curved line of the occiput. The 

 nerve supply is from the spinal accessory and the anterior divisions of 

 the second and third cervical nerves. The arterial supply is from the 

 occipital, the superior thyroid, through the descending branch (p. 28), 

 and the supra-scapular. 



The anterior border of the muscle is the surgeon's guide in ligation 

 of the common, external, or internal carotid artery, and in cesophago- 

 tomy ; and the posterior border of its clavicular origin is the guide to 

 the subclavian artery. 



The chief action of the muscle is to draw the head down to the 

 shoulder, and to turn the face to the opposite side. And this is neces- 

 sarily the attitude of the head and face in that form of wry-neck which 

 is secondary to contraction of the muscle. The common cause of 

 congenital wry-neck is rupture of one or both heads of the sterno- 

 mastoid during parturition, when the escaping head receives a vigo- 

 rous and natural twist ; the fibrous tissue by which the tear of the 

 muscular fibres is mended undergoes subsequent contraction. The 

 permanent drag upon that side of the face and head not only draws 

 down the corner of the mouth, the outer commissure of the eyelids, 

 and the side of the lower jaw, but also prevents the proper develop- 

 ment of the bones of that side of the face. In due course other muscles 

 and bands are shortened on the concave side of the neck, and the cer- 

 vical vertebrae become deformed. 



Relations. The sterno-mastoid is covered by the platysma ; the 

 external jugular vein ; lesser occipital, great auricular, and transverse 

 cervical nerves, and the deep fascia. 



Beneath it are another layer of the deep fascia, the sterno-hyoid, 



B2 



