40 ANATOMY OF THE HEAD AND NECK 



will be found lying upon the upper part of the posterior border of the 

 sterno-mastoid muscle. It is distributed to the integument of the 

 occipital region, and anastomoses with the occipitalis major, auricularis 

 magnus, and posterior branches of the facial nerve. 



The descending branches of the cervical plexus come from the third 

 and fourth cervical nerves, and, descending between the sterno-mastoid 

 and trapezius muscles, are named acromial and clavicular, being dis- 

 tributed to the integument and muscles of the shoulder and anterior 

 and upper part of the thorax. The deep branches will be described 

 hereafter. They are chiefly musciilar, or connecting filaments with 

 the pneumogastric, sympathetic, or hypoglossal nerves. The com- 

 municans noni aud the phrenic are the most important. 



The STERNO-MASTOID MUSCLE is the large and prominent 

 muscle which characterizes the cervical region ; it is en- 

 cased by the cervical fascia, and is crossed superficially by 

 the external jugular vein and the branches of the cervical 

 plexus. It arises by two heads, separated by an elongated 

 interval ; one, narrow, from the upper bone of the sternum 

 the other, broader, from the sternal third of the clavicle ; 

 the extent of the clavicular attachment varies, and in some 

 bodies may reach even to the trapezius muscle. These two 

 heads unite at about the middle of the neck in a rounded 

 belly, which is inserted into the mastoid process, and by a 

 broad and thin aponeurosis into the superior curved line of 

 the occipital bone. 



The OMO-HYOID MUSCLE is a small muscle which traverses 

 the neck diagonally, in a direction crossing that of the 

 sterno-mastoid, beneath which it lies; it is composed of 

 two bellies, united in the middle b}^ a tendon of variable 

 length ; only one portion of the muscle can be well seen 

 in the present stage of the dissection. It arises from the 

 scapula at the outside of, and sometimes in part from, the 

 transverse ligament stretching across the supra-scapular 

 notch ; it then passes forward, obscured from sight by the 

 clavicle; behind the sterno-mastoid, the scapular portion 

 terminates in a tendon which plays through a loop formed 

 by the deep cervical fascia, this loop being attached to the 

 cartilage of the first rib. From this intervening tendon 

 commences another belly, which pursues a direction up- 

 ward and forward, to be inserted into the hyoid bone at 

 the point of union between its body and the greater cornu. 

 Occasionally-, one of the bellies of this muscle is wanting, 

 and the whole muscle may be absent. 



The sterno-mastoid and the omo-hyoid muscles divide the 

 quadrilateral cervical region into " triangles," con venient for 



