

THE TRIANGLES OF TH1 



from the angle of the mandible to the mastoid process ; below, by the upper border 

 of the clavicle; in front, by the middle line of the neck; behind, by the anterior 

 margin of the Trapezius. This space is subdivided into two large triangles by the 

 Sternocleidomastoideus, which passes obliquely across the neck, from the sternum 

 and clavicle below, to the mastoid process and occipital bone above. The triangular 

 space in front of this muscle is called the anterior triangle ; and that behind it, the 

 posterior triangle. 



Anterior Triangle. The anterior triangle is bounded, in front, by the middle line 

 of the neck; behind, by the anterior margin of the Sternocleidomastoideus; its 

 base, directed upward, is formed by the lower border of the body of the mandible, 

 and a line extending from the angle of the mandible to the mastoid process; its 

 apex is below, at the sternum. This space is subdivided into four smaller triangles 

 by the Digastricus above, and the superior belly of the Omohyoideus below. 

 These smaller triangles are named the inferior carotid, the superior carotid, the 

 submaxillary, and the suprahyoid. 



Suprahydid triangle 

 Submaxillary triangle 



Superior carotid triangle 



Inferior carotid triangle 



Occipital triangle 



Subclavian triangle 

 FIG. 512. The triangles of the neck. 



The Inferior Carotid, or Muscular Triangle, is bounded, in front, by the median 

 line of the neck from the hyoid bone to the sternum ; behind, by the anterior margin 

 of the Sternocleidomastoideus; above, by the superior belly of the Omohyoideus. 

 It is covered by the integument, superficial fascia, Platysma, and deep fascia, 

 ramifying in which are some of the branches of the supraclavicular nerves. Be- 

 neath these superficial structures are the Sternohyoideus and Sternothyreoideus, 

 which, together with the anterior margin of the Sternocleidomastoideus, conceal 

 the lower part of the common carotid artery. 1 This vessel is enclosed within its 

 sheath, together with the internal jugular vein and vagus nerve; the vein lies 

 lateral to the artery on the right side of the neck, but overlaps it below on the left 

 side; the nerve lies between the artery and vein, on a plane posterior to both. 



1 Therefore the common carotid artery and internal jugular vein are not, strictly speaking, contained in this tri- 

 angle, since they are covered by the Sternocleidomastoideus: that is to say, they lie under that muscle, which forms 

 the posterior border of the triangle. But as they lie very close to the structures which are really contained in the 

 triangle, and whose position it is essential to remember in operating on this part o/ the artery, it is expedient to study 

 the relations of all these parts together. 





