606 



THE VASCULAR SYSTEMS 



regions of the neck, in each of which important operations are constantly being 

 performed. 



The side of the neck presents a somewhat quadrilateral outline, limited, above, 

 by the lower border of the body of the mandible, and an imaginary line extending 

 from the angle of the mandible* to the mastoid process ; below, by the prominent 

 upper border of the clavicle; in front, by the median line of the neck; behind, by 

 the anterior margin of the Trapezius muscle. This space is subdivided into two 

 large triangles by the Sternomastoid muscle, which passes obliquely across the 

 neck, from the sternum and clavicle below to the mastoid process above. The 

 triangular space in front of this muscle is called the anterior triangle; and that 

 behind it, the posterior triangle. 



Suprahyoid triangle. 

 Submaxillary triangle. 



Superior carotid 

 triangle. 



Inferior carotid 

 triangle. 



Occipital triangle. 



Subclavian triangle. 

 FIG. 446. The triangles of the neck. 



% 



The anterior triangle is bounded, in front, by a line extending from the svmphy- 

 sis menti to the sternum; behind, by the anterior margin of the Sternomastoid; its 

 base, directed upward, is formed by the lower border oFthelbody of theTnandible 

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

 apex is below, at the sternum. This space is subdivided^ into four smaller tri- 

 angles by the Digastric muscle above and the anterior belly of the Omohyoid below. 

 These smaller triangles are named from below upward, the inferior carotid, the 

 superior carotid, the submaxillary, and the suprahyoid triangles. 



The inferior carotid triangle, or the triangle of necessity, is bounded, in front, by 

 the median line of the neck; behind, by the anterior margin of the Sternomastoid L 

 above, by the anterior belly of the Omohyoid: and is covered by the integument, 

 superficial fascia. Platysma. and deep fascia, ramifying between which are some 

 of the descending branches of the superficial cervical plexus. Beneath these 

 superficial structures are the Sternohyoid and Sternothyroid muscles, which, 

 together with the anterior margin of the Sternomastoid, conceal the lower part of 

 the common carotid artery. 1 The floor of this triangle is formed by the Longus 



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

 triangle, since they are covered by the Sternomastoid muscle; ^hat is to say, lie behind the anterior border 

 of 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 of the artery, it has seemed expedient to study the relations of all these parts together. 



