POSTERIOR TRIANGLE 37 



backwards, and disappears, through the floor of the triangle, 

 between the adjacent borders of the levator scapulae above and 

 the scalenus medius below. Above the dorsal scapular nerve 

 are the branches from the third and fourth cervical nerves to 

 the trapezius and the communications to the accessory nerve. 



When the structures mentioned above have been found and 

 cleaned, proceed to the dissection of the subclavian portion of 

 the triangle. Find the transverse scapular artery which lies 

 behind the clavicle, and therefore, strictly speaking, outside the 

 limits of the triangle. Then remove the second layer of deep 

 cervical fascia which binds the posterior belly of the omo-hyoid 

 to the posterior border of the clavicle, and find behind it : (i) a 

 further part of the external jugular vein ; (2) a further part of 

 the transverse cervical artery ; (3) the lower part of the nerve 

 to the subclavius ; (4) the upper portion of the third part of the 

 subclavian artery ; (5) the lowest root and the lower parts of 

 the trunks of the brachial plexus ; (6) a part of the long thoracic 

 nerve ; (7) inferior deep cervical lymph glands. 



First clean the lower end of the external jugular vein and 

 follow it behind the clavicle to its termination in the subclavian 

 vein. Note the valves near its lower end. Next clean the 

 transverse cervical artery and the nerve to the subclavius. 

 Follow the nerve to the subclavius across the front of the third 

 part of the subclavian artery ; and afterwards clean the lower 

 part of the subclavian artery and the adjacent part of the brachial 

 plexus, which lies behind and above the artery. Note that the 

 artery and the plexus are covered by a layer of deep cervical 

 fascia, the backward prolongation of the prevertebral layer of 

 fascia, which passes on to them from the lateral border of the 

 scalenus anterior, which lies deep to the posterior border of the 

 sterno-mastoid. The fascia is prolonged along the plexus and 

 the artery to become continuous with the sheath of the axillary 

 artery. 



As the areolar tissue is cleared from the subclavian portion 

 of the triangle a number of inferior deep cervical lymph glands 

 may be noted. They receive lymph from the axillary glands, 

 and they transmit it to the large lymph vessels at the root of 

 the neck (Fig. 14, p. 29, Vol. I.). 



After the contents of the lower part of the triangle are 

 thoroughly cleaned, remove the remains of the fascia covering 

 the muscles which form the floor of the triangle. Note that 

 that fascia is continuous anteriorly, round the tips of the trans- 

 verse processes of the cervical vertebrae, with the prevertebral 

 fascia. Posteriorly, it blends with the sheaths of the deeper 

 muscles at the back of the neck ; above, it is attached to the 

 superior nuchal line ; and below, as already stated, it is pro- 

 longed into the axilla along the axillary vessels and nerves. 



Boundaries and Contents of the Posterior Triangle. The 



dissection of the triangle should be completed in two days. 

 On the third day the dissector should revise his knowledge 

 of the boundaries and the relative positions of the contents. 



The triangle is bounded anteriorly by the posterior border 

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

 in 3 b 



