THE TRIANGLES OF THE NECK 565 



vagus nerve, separated from the external carotid by the Styloglossus and Stylo- 

 pharyngeus, and the glossopharyngeal nerve. 1 



The Suprahyoid Triangle is limited behind by the anterior belly of the Digastricus, 

 in front by the middle line of the neck between the mandible and the hyoid bone ; 

 below, by the body of the hyoid bone; its floor is formed by the Mylohyoideus. 

 It contains one or two lymph glands and some small veins; the latter unite to form 

 the anterior jugular vein. 



Posterior Triangle. The posterior triangle is bounded, in front, by the Sterno- 

 cleidomastoideus ; behind, by the anterior margin of the Trapezius ; its base is formed 

 by the middle third of the clavicle; its apex, by the occipital bone. The space 

 is crossed, about 2.5 cm. above the clavicle, by the inferior belly of the Omo- 

 hyoideus, which divides it into two triangles, an upper or occipital, and a lower or 

 subclavian. 



The Occipital Triangle, the larger division of the posterior triangle, is bounded, 

 in front, by the Sternocleidomastoideus; behind, by the Trapezius; below, by the 

 Omohyoideus. Its floor is formed from above downward by the Splenius capitis, 

 Levator scapulae, and the Scaleni medius and posterior. It is covered by the skin, 

 the superficial and deep fasciae, and by the Platysma below. The accessory nerve 

 is directed obliquely across the space from the Sternocleidomastoideus, which it 

 pierces, to the under surface of the Trapezius; below, the supraclavicular nerves 

 and the transverse cervical vessels and the upper part of the brachial plexus cross 

 the space. A chain of lymph glands is also found running along the posterior border 

 of the Sternocleidomastoideus, from the mastoid process to the root of the neck. 



The Subclavian Triangle, the smaller division of the posterior triangle, is bounded, 

 above, by the inferior belly of the Omohyoideus; below, by the clavicle; its base is 

 formed by the posterior border of the Sternocleidomastoideus. Its floor is formed 

 by the first rib with the first digitation of the Serratus anterior. The size of the 

 subclavian triangle varies with the extent of attachment of the clavicular portions 

 of the Sternocleidomastoideus and Trapezius, and also with the height at which 

 the Omohyoideus crosses the neck. Its height also varies according to the position 

 of the arm, being diminished by raising the limb, on account of the ascent of the 

 clavicle, and increased by drawing the arm downward, when that bone is depressed. 

 This space is covered by the integument, the superficial and deep fasciae and the 

 Platysma, and crossed by the supraclavicular nerves. Just above the level of the 

 clavicle, the third portion of the subclavian artery curves lateral ward and downward 

 from the lateral margin of the Scalenus anterior, across the first rib, to the axilla, 

 and this is the situation most commonly chosen for ligaturing the vessel. Some- 

 times this vessel rises as high as 4 cm. above the clavicle; occasionally, it passes 

 in front of the Scalenus anterior, or pierces the fibers of that muscle. The sub- 

 clavian vein lies behind the clavicle, and is not usually seen in this space; but in 

 some cases it rises as high as the artery, and has even been seen to pass with that 

 vessel behind the Scalenus anterior. The brachial plexus of nerves lies above 

 the artery, and in close contact with it. Passing transversely behind the clavicle 

 are the transverse scapular vessels; and traversing its upper angle in the same 

 direction, the transverse cervical artery and vein. The external jugular vein runs 

 vertically downward behind the posterior border of the Sternocleidomastoideus, 

 to terminate in the subclavian vein; it receives the transverse cervical and trans- 

 verse scapular veins, which form a plexus in front of the artery, and occasionally 

 a small vein which crosses the clavicle from the cephalic. The small nerve to the 

 Subclavius also crosses this triangle about its middle, and some lymph glands are 

 usually found in the space. 



1 The remark made about the inferior carotid triangle applies also to this one. The structures enumerated as con- 

 tained in its posterior part lie, strictly speaking, beneath the muscles which form the posterior boundary of the tri- 

 angle; but as it is very important to bear in mind their close relation to the parotid gland, all these parts are spoken 

 of together. 



