42 THE UPPER EXTREMITY 



the acromion and the upper margin of the spine of the 

 scapula ; while the lower thoracic fibres are directed upwards 

 and, at the base of the scapula, end in a flat, triangular 

 tendon, which plays over the smooth surface at the root of 

 the scapular spine, and is inserted into a rough tubercle on 

 the spine of the scapula immediately beyond this (Fig. 24, 

 p. 55). To facilitate the movement of the tendon upon the 

 bone a small bursa mucosa is interposed between them. 



The trapezius is supplied by the accessory nerve and by 

 twigs from the third and fourth cervical nerves. It is an 

 elevator and depressor of the shoulders, and an adductor 

 of the scapula. 



Dissection. The latissimus dorsi is now to be dissected. It is a difficult 

 muscle to clean, not only on account of the varying direction of its fibres, 

 but also because its upper part is generally very thin, and its upper border 

 ill -defined. Near the spines of the vertebrae its upper portion is overlapped 

 by the trapezius, but in the greater part of its extent it is subcutaneous. 

 Both layers of fascia should be raised at the same time from its surface, and 

 its fibres may be stretched by raising the arm and folding it under the neck. 

 The origin of the latissimus dorsi in the lumbar region is effected through 

 the medium of the superficial lamina of the lumbar fascia, a dense tendinous 

 aponeurosis, which covers the sacrospinalis in the loins (Fig. 19). Clean 

 this structure thoroughly. The attachment of the muscle to the crest of 

 the ilium, and its slips of origin from the lower ribs, -must be carefully 

 defined ; at the same time, the posterior and lower part of the external 

 oblique muscle of the abdomen should be cleaned, so that its relation to 

 the latissimus dorsi may be studied. As the latissimus dorsi sweeps over 

 the inferior angle of the scapula it receives an accession of fibres from that 

 bone. This fleshy slip may be brought into view, when the muscle is 

 cleaned, by relieving the tension of the muscular fibres, and then turning 

 the upper margin of the muscle laterally. The slip in question is apt to 

 be mistaken for a piece of the teres major muscle upon which it lies. 



M. Latissimus Dorsi. The latissimus dorsi is a wide, flat 

 muscle, which covers the back from the level of the sixth 

 thoracic vertebra down to the crest of the ilium (Fig. 1 7, p. 39). 

 It arises (i) from the tips of the spinous processes of the 

 lower six thoracic vertebrae and the supraspinous ligaments in 

 connection with them; (2) from the superficial lamella of 

 the fascia lumborum (Fig. 19); (3) by a thin tendinous origin 

 from a small extent of the lateral lip of the crest of the ilium in 

 front of the fascia lumborum (Fig. 143, p. 385); (4) by three 

 or four digitations from the lower three or four ribs ; and (5) 

 by a fleshy slip from the dorsal aspect of the inferior angle 

 of the scapula (Fig. 24, p. 55). By means of its origin from 

 the posterior lamella of lumbar fascia, it receives an indirect 

 attachment to the spines of the lumbar and upper sacral 



