POSTERIOR TRIANGLE 149 



The triangle is bounded anteriorly by the posterior border 

 of the sterno-mastoid ; posteriorly by the anterior border of the 

 trapezius ; below by the upper border of the middle third 

 of the clavicle ; and above by the superior nuchal line of the 

 occipital bone, or by the meeting of the upper ends of the sterno- 

 mastoid and the trapezius. The roof is formed by the deep 

 cervical fascia, which is covered by superficial fascia and skin, 

 and in its lower and anterior part by the platysma, which is 

 embedded in the superficial fascia. It is pierced by (i) the 

 external jugular vein at the lower and anterior angle; (2) the 

 supraclavicular nerves, a short distance above the clavicle ; 

 (3) small cutaneous branches of the transverse scapular, trans- 

 verse cervical, and occipital arteries; (4) lymphatic vessels 

 passing from the superficial structures to the glands in the 

 triangle. It is frequently stated that the small occipital, the 

 great auricular, and the cervical cutaneous nerves also 

 pierce the roof. As a general rule they turn round the 

 posterior border of the sterno-mastoid under cover of the 

 fascia, and pierce the fascia as it lies on the muscle. 



The floor is formed by the splenius capitis, the levator 

 scapulae, the scalenus medius, and the scalenus posterior 

 muscles, with the addition, occasionally, of a small part of the 

 semispinalis capitis (O.T. complexus) above, and the upper 

 serration of the serratus anterior below ; the latter appears 

 in the area of the triangle only when the clavicle is very 

 fully depressed. The muscles of the floor are covered with 

 a layer of fascia which is the backward continuation of the 

 prevertebral fascia of the anterior cervical region. 



The contents of the posterior triangle are : 



1. Fatty areolar tissue. 



2. The posterior belly of the omo-hyoid muscle. 



3. Lymph ( Post sterno-mastoid. 



Glands, ( Supraclavicular. 



( Third part of subclavian. 



... ! ! Transverse cervical and its terminal branches. 

 4-- /\rieries. i ,-\ . / . \ 

 I Occipital (sometimes). 



f External jugular. 

 I Transverse cervical. 



5. Veins,' 2 "j Transverse scapular (O.T. suprascapular). 

 ^Termination of anterior jugular. 



1 The transverse scapular artery (O.T. suprascapular) lies posterior to 

 the clavicle and is not, strictly speaking, in the triangle. 



2 The subclavian vein is posterior to the clavicle and therefore is not 

 contained within the triangle. 



ii 10 & 



