THE POSTERIOR TRIANGULAR SPACE. 575 



plexuses, with the portion of the subclavian artery and some 

 H'sets nf the vessel and the nerves. 



Dissection. l>y the removal of the cervical fascia and the fat Dissection 

 between the sterno-mastoid and trapezius muscles, the posterior 

 trlmgle of the neck will be displayed. In the execution of this 

 somewhat difficult task the student should proceed cautiously, to 

 avoid injuring the numerous nerves and vessels in the space. 



Seek first the small omo-hyoid muscle (fig 210 3 ), which crosses Find 

 the space obliquely about an inch above the clavicle, and divides it or 

 into two smaller triangles, occipital and supra clavicular (fig. 209). 

 Close to or beneath the upper border of the muscle lie the slender 

 nerve and vessels to it : the nerve is derived from the ansa 

 hypoglossi, and the artery from the suprascapular. 



Above the omo-hyoid muscle will be found the branches of the Nerves 

 cervical plexus, together with the spinal accessory nerve ; the latter omo-hyoid ; 

 will be recognised by its piercing the sterno-mastoid muscle. The 

 greater number of the branches of the cervical plexus descend to the 

 shoulder ; but the small occipital and great auricular nerves ascend 

 to the head, and the superficial cervical branch is directed forwards 

 over the sterno-mastoid muscle. 



Below the omo-hyoid find the large subclavian artery and the vessels 

 brachial plexus, which have a deep position, and run downwards 

 and outwards. Also the following vessels and nerve are to be 

 further cleaned, viz., the suprascapular vessels behind the clavicle ; 

 the tr msverse cervical vessel, which is higher in the neck, taking 

 an outward direction beneath the omo-hyoid muscle ; and, lastly, 

 the small branch of nerve to the subclavius muscle, which lies and a small 

 about the middle of the space between the clavicle and the 

 omo-hyoid. 



Underneath the trapezius, where it is attached to the clavicle, Define 

 define the uppermost digitation of the serratus magnus muscle ; and se us ' 

 behind the brachial plexus, towards the lower part of the space, the 

 middle scalenus muscle appears. Through the scalenus issue two and nerves 

 muscular nerves ; one, the long thoracic, formed by two or three 

 roots, for the serratus magnus ; the other smaller, and higher up, 

 for the rhomboidei. 



Limits of the space. The space is bounded in front by the sterno- Boundaries, 

 mastoid muscle ( x ), and behind by the trapezius (a). Its base corre- 

 sponds with the middle third of the clavicle, and its apex is at the 

 skull. In its floor are several muscles, which are placed in the 

 following order from above downwards, viz., splenius capitis, levator, 

 anguli scapulae ( 6 ), and middle scalenus ( 5 ) ; and at the lower and 

 outer angle, somewhat beneath the trapezius, lies the upper part of 

 the serratus magnus. Covering the space are the structures already 

 examined, viz., the skin and superficial fascia, the platysnia over the 

 lower half or two-thirds, and the deep fascia. 



The small omo-hyoid muscle ( 3 ) crosses the space near the clavicle, j s divided 

 so as to divide it into two, a lower or supraclavicular triangle, and-Jy 0- 

 an upper or occipital (fig. 209). 



The supraclavicular triangle is the smaller, and contains the sub- 



