POSTERIOR TRIANGLE 147 



borders of the trapezius and the sterno-mastoid, or pierces the trapezius a 

 little further posteriorly. 



Between the accessory nerve above and the posterior belly of the omo- 

 hyoid below find (i) the upper part of the brachial plexus ; (2) its branch 

 to the subclavius ; (3) its suprascapular branch ; (4) its dorsalis scapulae 

 branch; (5) its long thoracic branch; (6) branches from the third and 

 fourth cervical nerves to the levator scapulae ; (7) branches from the third 

 and fourth cervical nerves to the trapezius, and others which communicate 

 with the accessory nerve in the posterior triangle ; and (8) the upper and 

 posterior part of the transverse cervical artery. Find the transverse cervical 

 artery as it appears from under cover of the upper border of the omo-hyoid. 

 It runs upwards and posteriorly. Next secure the nerve to the subclavius, 

 which lies under cover of the deep fascia above the omo-hyoid and a short 

 distance behind the sterno-mastoid. Trace it upwards to its origin from 

 the trunk formed by the union of the fifth and sixth cervical nerves. Clean 

 the latter nerves and the upper part of the seventh cervical nerve, which 

 lies immediately below them. Then find the suprascapular nerve, which 

 springs from the lateral border of the trunk formed by the fifth and sixth 

 nerves. It lies immediately above the anterior part of the posterior belly 

 of the omo-hyoid, and disappears under cover of the posterior part. 

 Turn the trunk formed by the fifth and sixth cervical nerves anteriorly and 

 find, posterior to it, the upper roots of the long thoracic nerve, which spring 

 from the fifth and sixth nerves, and are emerging through the fibres of the 

 scalenus medius muscle. The nervus dorsalis scapulae (O.T. nerve to the 

 rhomboids) lies at a slightly higher level than the suprascapular nerve. It 

 springs from the fifth cervical nerve, runs downwards and posteriorly, 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 (O.T. suprascapular), 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) supraclavicular 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, and is prolonged 

 along them 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 supraclavicular 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. 

 II 10 a 



