THE ANTERIOR TRIAXGLE OF THE NECK. 563 



obliquely downward and forward along the septum nasi, supplies the mucous 

 membrane, and anastomoses in front with the terminal branch of the descending 

 palatine. The external branches, two or three in number, supply the mucous 

 membrane covering the lateral wall of the nose, the antrum, and the ethmoid and 

 sphenoid cells. 



SURGICAL ANATOMY OF THE TRIANGLES OF THE NECK. 



The student having considered the relative anatomy of the large arteries of the 

 neck and their branches, and the relations they bear to the veins and nerves, should 

 now examine these structures collectively, as they present themselves in certain 

 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 jaw, and an imaginary line extending from 

 the angle of the jaw 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 Sterno-niastoid 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 trianyh-. 



ANTERIOR TRIANGLE OF THE NECK. 



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

 to the sternum : behind, by the anterior margin of the Sterno-mastoid ; its base, 

 directed upward, is formed by the lower border of the body of the jaw and a line 

 extending from the angle of the jaw to the mastoid process ; its apex is below, at 

 the sternum. This space is subdivided into three smaller triangles by the Digastric 

 muscle above and the anterior belly of the Omo-hyoid below. These smaller 

 triangles are named, from below upward, the inferior carotid, the superior carotid, 

 and the submaxillary triangle. 



The Inferior Carotid Triangle is bounded, in front, by the median line of the 

 neck ; behind, by the anterior margin of the Sterno-mastoid ; above, by the anterior 

 belly of the Omo-hyoid ; and is covered by the integument, superficial fascia, 

 Platysma. and deep fascia, ramifying between which is the descending branch of 

 the superficialis colli nerve. Beneath these superficial structures are the Sterno- 

 hyoid and Sterno-thyroid muscles, which, together with the anterior margin of 

 the Sterno-mastoid, conceal the lower part of the common carotid artery. 1 



This vessel is enclosed within its sheath, together with the internal jugular 

 vein and pneumogastric nerve ; the vein lying on the outer side of the artery on 

 the right side of the neck, but overlapping it, or passing directly across it on the 

 left side ; the nerve lying between the artery and vein, on a plane posterior to 

 both. In front of the sheath are a few filaments descending from the loop of com- 

 munication between the descendens and communicans hypoglossi ; behind the sheath 



-een the inferior thyroid artery, the recurrent laryngeal nerve, and the sym- 

 pathetic nerve ; and on its inner side, the trachea, the thyroid gland much more 

 prominent in the female than in the male and the lower part of the larynx. By cut- 

 ting into the upper part of this space and slightly .displacing the Sterno-mastoid 

 muscle the common carotid artery may be tied below the Omo-hyoid muscle. 



The floor of the inferior carotid triangle is formed by the Longus colli muscle 

 below, by the Scalenus anticus above (see Fig. 284. page 424), between which 



1 Therefore the common carotid artery and internal jugular vein are not, strictly speaking, con- 

 tained in this triangle, since they are covered by the Sterno-mastoid muscle ; that 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. 



