410 



THE MUSCLES AND FASCIA. 



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. 276. Muscles of the neck and boundaries of the triangles. 



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 



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 artery, internal jugular vein, commencement of the internal and 

 external carotid arteries, the occipital, subclavian, transversalis colli, and supra- 

 scapular arteries and veins ; the pneumogastric, hypoglossal, descendens and 

 communicans hypoglossi nerves, and the spinal accessory nerve, which pierces 

 its upper third ; the cervical plexus, part of the parotid gland and deep lymphatic 

 glands. 



Nerves. The Platysma myoides is supplied by the facial and superficial 

 branches of the cervical plexus ; the Sterno-cleido-mastoid, by the spinal accessory 

 and deep branches of the cervical plexus. 



Actions. When only one Sterno-mastoid muscle acts, it flexes the head and 

 draws it toward the shoulder of the same side, assisted by the Splenius and the 

 Obliquus capitis inferior of the opposite side. At the same time it rotates the head 

 so as to carry the face toward the opposite side. When both muscles are brought 



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

 neck. 



