THE SUPERFICIAL CERVICAL REGION. 409 



symphysis of the inferior maxilla, and, lower down, to the hyoid bone, between 

 which points it is thin ; below the hyoid bone it becomes thicker, and is attached 

 below to the anterior margin of the upper border of the sternum. The layer 

 of the deep cervical fascia which passes under the Sterno-mastoid covers the 

 anterior surface of the Scalenus anticus muscle. At the outer side of the 

 carotid vessels it divides into two, one layer passing in front of the vessels, the 

 other behind them. The layer which passes in front of the vessels again divides 

 into three lamella*. Of these, the anterior lamella, except for an inch below 

 where it forms the posterior boundary of Burns's space, joins the layer of cervical 

 fascia passing over the Sterno-mastoid, and with it passes to the middle line 

 covering the anterior surface of the Depressor muscles of the hyoid bone. The 

 portion of this lamella which invests the Omo-hyoid is continued downward as a 

 distinct process, which descends to be inserted into the sternum and cartilage of 

 the first rib. and becomes connected with the Costo-coracoid membrane. The 

 middle lamella passes behind the depressors of the hyoid bone and in front of the 

 thyroid body to meet its fellow of the opposite side, in front of the trachea. At 

 the root of the neck this middle lamella can be traced downward into the thorax 

 to become continuous with the fibrous layer of the- pericardium. The posterior 

 lamella passes over to the inner side of the carotid vessels, and joins the layer 

 passing behind them, thus enclosing them in a sheath. The layer of cervical 

 fascia which passes behind the carotid vessels, having been joined by the posterior 

 of the three lamellae from the layer of fascia passing in front of the vessels, is 

 prolonged inward, behind the pharynx and oesophagus, forming a sheath for the 

 Prevertebral muscles, the prevertebral fascia. The layer of the deep cervical 

 fascia, which passes behind the Sterno-mastoid, gives off another lamella, which 

 passes downward and outward over the brachial plexus and subclavian vessels, to 

 assist in forming the axillary sheath. The two layers of the deep cervical fascia, 

 where they unite opposite the angle of the lower jaw, bind the Sterno-mastoid 

 muscle to this part of the bone. From that portion of the cervical fascia which 

 is attached to the angle of the jaw a process of extreme density is found passing 

 behind to the inner side of the parotid gland, to be attached to the apex of the 

 styloid process of the temporal bone ; this is termed the Stylo-maxillary liga- 

 ment. 



The Sterno-mastoid or Sterno-cleido-mastoid < Fig. 276) is a large, thick muscle, 

 which passes obliquely across the side of the neck, being enclosed between the two 

 layers of the deep cervical fascia. It is thick and narrow at its central part, but is 

 broader and thinner at each extremity. It arises, by two heads, from the sternum 

 and clavicle. The sternal portion is a rounded fasciculus, tendinous in front, fleshy 

 behind, which arises from the upper and anterior part of the first piece of 

 the sternum, and is directed upward, outward, and backward. The clavicular 

 portion arises from the inner third of the superior border of the clavicle, being 

 composed of fleshy and aponeurotic fibres : it is directed almost vertically upward. 

 These two portions are separated from one another, at their origin, by a triangular 

 cellular interval, but become gradually blended, below the middle 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 border, 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 attachment to the clavicle : 

 in one case the clavicular may be as narrow as the sternal portion ; in another, - 

 as much as 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 sub- 

 clavian 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 



