500 THE BLOOD-VASCULAR SYSTEM. 



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-mastoid 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. 



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 are some of the descending 

 branches of the superficial cervical plexus. Beneath these superficial structures 

 are the Sterno-hyoid and Sterno-thyroid muscles, which, together with the anter- 

 ior 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 below 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 communication between the 

 descendens and communicans hypoglossi ; behind the sheath are seen the inferior 

 thyroid artery, the recurrent laryngeal nerve, and the sympathetic 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 cutting 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 Superior Carotid Triangle is bounded, behind, by the Sterno-mastoid ; 

 below, by the anterior belly of the Omo-hyoid ; and above, by the Posterior belly 

 of the Digastric muscle. It is covered by the integument, superficial fascia, 

 Platysma, and deep fascia, ramifying between which are branches of the facial 

 and superficial cervical nerves. Its floor is formed by parts of the Thyro-hyoid, 

 Hyo-glossus, and the inferior and middle Constrictor muscles of the pharynx. 

 This space, when dissected, is seen to contain the upper part of the common carotid 



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. 



