856 DISSECTION OF THE BACK. 



The spinal accessory cranial nerve (p. 114), having crossed the poste- 

 rior triangle of the neck, passes beneath the trapezius, and forms a plexi- 

 form union with branches of the third and fourth nerves of the cervical 

 plexus. The nerve is distributed nearly to the lower border of the muscle. 



Dissection. To see the parts covered by the trapezius, the pieces of 

 the divided muscle are to be thrown inwards and outwards. 



The dissector of the neck should now clean the splenius, and define the 

 parts beneath the clavicle, viz. the posterior belly of the omo-hyoid mus- 

 cle with the suprascapular nerve and vessels ; the transverse cervical ves- 

 sels ; and the small branches of nerves to the levator anguli scapulae, and 

 rhomboid muscles. If the trapezius be detached along the middle line, the 

 ligamentum nuchre, from which it takes origin, will be brought into view. 



* The dissector of the, upper limb should clean the fibres of the rhom- 

 boidei and levator anguli scapulae muscles, which are fixed to the base of 

 the scapula ; and whilst this is being done, the scapula is to be drawn 

 a\\ay from the trunk to make tense the fleshy fibres. 



* Parts covered by the trapezi'is. The trapezius conceals in the neck 

 the splenius, a small part of the complexus, and the levator anguli scapu- 

 lae ; in the dorsal region it covers the following muscles, the rhomboidei, 

 the erector spinae, and the latissimus dorsi. Near the insertion it lies over 

 the supraspinatus muscle. 



The ligamentum nuchce is a narrow fibrous band, which extends from the 

 spinous process of the seventh cervical vertebra to the occipital protuber- 

 ance. From its under part processes are attached to the spines of the 

 six lower cervical vertebrae, so that it serves as a partition between the 

 muscles of the opposite sides of the neck. In man it is not formed of elas- 

 tic tissue. 



* The LATISSIMUS DORSI (fig. 116, B ) is the widest muscle in the back, 

 and is thin and aponeurotic at its inner attachment. It arises along the 

 middle line from the spinous processes of the six lower dorsal, all the lum- 

 bar, and the upper two sacral vertebras, as well as from the supraspinous 

 ligament. On the outer side it arises by an aponeurosis from the outer 

 edge of the posterior half of the iliac crest ; and by three or four fleshy 

 processes from as many of the lower ribs, which digitate with pieces of the 

 external oblique muscle of the abdomen. And between the outer and 

 inner attachments it is inseparably blended below with the subjacent ten- 

 don of the multifidus spinge. All the fibres converge to the inferior angle 

 of the scapula, and after crossing that point of bone, are continued for- 

 wards to be inserted by tendon into the bottom of the bicipital groove of 

 the humerus (p. 236). 



The muscle is subcutaneous, except a small part of the upper border 

 which is covered by the trapezius. Near the scapula there is a space be- 

 tween the two, in which the rhomboid muscles appear. The lower or 

 anterior overlays the edge of the external oblique muscle of the abdominal 

 wall in the interval between the last rib and the iliac crest, with the ex- 

 ception of a small part below. Frequently the latissimus has a distinct 

 fleshy slip from the inferior angle of the scapula. 



Action. If the arm is hanging loose the muscle can move it behind the 

 back, rotating it in at the same time. If the limb is raised, the latissimus, 

 combining with the pectoralis and teres, will depress the humerus. From 

 its attachment to the scapula this bone can be depressed with the arm. 



Supposing the arm fixed, the fibres may elevate the ribs as an inspira- 



