POSTERIOR TRIANGLE 145 



transverse cervical, transverse scapular (O.T. suprascapular), 

 and occipital arteries, and, occasionally, by the occipital artery 

 itself. It is not a very strong layer, and it is frequently difficult 

 to display it as a continuous sheet. Over the upper part of the 

 triangle it forms a single layer, but below, it splits into two 

 lamellae, a superficial and a deep. The superficial layer which 

 is already displayed, is attached to the upper border of the 

 clavicle from the sterno-mastoid anteriorly to the trapezius 

 posteriorly. It is pierced by the external jugular vein and 

 the supraclavicular nerves. 



Dissection. Trace the supraclavicular nerves upwards through the deep 

 fascia to the posterior border of the sterno-mastoid ; then, pulling them aside, 

 cut through the superficial layer of the deep fascia immediately above the 

 clavicle and along the posterior border of the sterno-mastoid, and turn it 

 upwards. Introduce the handle of the scalpel behind the clavicle and note 

 that it can be passed downwards as far as the posterior border of the lower 

 surface of the bone. Its further progress is barred by the attachment of 

 the second layer of the deep fascia to this border, where it blends with the 

 posterior lamella of the costo-coracoid membrane. Pass the handle of the 

 knife forwards behind the sterno-mastoid and note that, without using any 

 great force, it can be pushed medially until it crosses the median plane ; 

 therefore, the space between the two layers of deep fascia in the lower part 

 of the posterior triangle is continuous anteriorly with the space which lies 

 above and posterior to the manubrium sterni, between the first and the second 

 layers of the deep fascia of the anterior part of the neck. Laterally, this 

 space extends as far as the coracoid process, and upwards to a short distance 

 above the posterior belly of the omo-hyoid muscle. Clear away the areolar 

 tissue which lies between the two layers of the deep fascia, and expose a 

 further part of the external jugular vein, and the terminal parts of the 

 transverse cervical and the transverse scapular (suprascapular) veins, as 

 they join the posterior border of the external jugular. Pull the lower part 

 of the external jugular vein posteriorly and expose the termination of the 

 anterior jugular vein in its anterior border. Dissect carefully behind the 

 clavicle and find the transverse scapular (suprascapular) artery. Trace the 

 second layer of the deep fascia upwards and note that it is continuous with 

 the fascia which surrounds the posterior belly of the omo-hyoid muscle ; 

 indeed it is the tension of this portion of the deep fascia which holds the 

 posterior belly of the muscle down in its position. 



Remove the remaining parts of the deep fascia, first from the upper, 

 and then from the lower part of the triangle, and expose the floor and the 

 remaining contents of the triangle. 



Commence above, in the region of the junction of the upper third and 

 the lower two-thirds of the posterior border of the sterno-mastoid, and 

 secure the great auricular, the small occipital, the accessory nerve, and the 

 nervus cutaneus colli. The great auricular is most easily found. It turns 

 round the posterior border of the sterno-mastoid, in the region indicated, 

 and runs upwards and anteriorly, parallel with and slightly above and 

 posterior to the external jugular vein. The small occipital will lie found 

 hooking round the lower border of the accessory nerve a little above the 

 great auricular ; and the nervus cutaneus colli lies a little below the great 

 auricular. 



Follow the small occipital and the great auricular nerves to their 



VOL. II 10 



