318 



THE MUSCLES AND FASCIAE. 



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 



FIG. 202. Muscles of the neck and boundaries of the triangles. 



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

 the triangle is at the upper border of the sternum. The boundaries of the 

 posterior triangle are, in front, the posterior border of the Sterno-mastoid ; below, 

 the middle third of the clavicle ; behind, the anterior margin of the Trapezius. 1 

 The apex corresponds with the meeting of the Sterno-mastoid and Trapezius on 

 the occipital bone. 



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

 from which it is separated by the external jugular vein, the superficial branches 

 of the cervical plexus, and the anterior layer of the deep cervical fascia. By its 

 deep surface it is in relation with the Sterno-clavicular articulation ; a process of 

 the deep cervical fascia ; the Sterno-hyoid, Sterno-thyroid, Omo-hyoid, posterior 

 belly of the Digastric, Levator anguli scapulae, Splenius and Scaleni muscles ; 

 common carotid artei'y, internal and anterior jugular veins, commencement of the 

 internal and external carotid arteries, the occipital, subclavian, transversalis colli, 

 and suprascapular arteries and veins ; the phrenic, pneumogastric, hypoglossal, 

 descendens and communicans hypoglossi nerves ; the spinal accessory nerve, which 



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

 neck. 



