TRIANGLES OF THE NECK. 485 



On the outside of the mastoid muscle, and between its 

 posterior edge and the anterior edge of the trapezius, there 

 is another triangular space, having its base below, resting 

 on the clavicle its apex above, at the mastoid process, 

 where the muscles meet, while its sides are formed by the 

 same muscles. This space is called the posterior lateral 

 triangle of the neck. 



Each of these large triangular spaces is crossed by the 

 omo-hyoideus muscle, which divides each of them into 

 two, and consequently makes four triangles on each side 

 of the median line of the neck. These are named as fol- 

 lows : 1. Anterior superior. 2. Anterior inferior. 3. Pos- 

 terior superior. 4. Posterior inferior. 



Of these triangles, the anterior superior and posterior 

 inferior seem, practically, the most important, as in the 

 former we tie the carotid artery, and in the latter, the 

 subclavian. It may be well here to notice the contents of 

 each of these triangles. 



The anterior superior triangle is situated between the 

 anterior belly of the omo-hyoid, and the sterno mastoid, the 

 apex of the triangle being formed by the intersection of 

 these muscles opposite the cricoid cartilage, and the base, 

 which is superior, by the digastric muscle. The carotid 

 artery, the internal jugular vein, the par-vagum, and the 

 sympatlietic nerves, are found in this triangle, simply cov- 

 ered by the fascia, the platysma, and the integuments. 



The anterior inferior triangle is situated below the ante- 

 rior belly of the orno-hyoid, and between it and the median 

 line of the neck, above the sternal end of the clavicle ; it 

 also contains the carotid artery, the jugular vein, and the 

 accompanying nerves, and is covered by the sterno-mastoid, 

 sterno-hyoid, and sterno-thyroid muscles. A portion of 

 the thyroid gland is also seen in this triangle. 



The posterior superior triangle is between the trapezius 

 and sterno-mastoid, and above the posterior belly of the 

 omo-hyoid muscle; it contains cellular tissue, lymphatic 

 glands, and the cervical plexus of nerves. 



The posterior inferior triangle is below the posterior belly 



