44 THE UPPER EXTREMITY 



the teres major, then it is folded round its distal border, and 

 finally it is inserted in front of it. To this peculiar relation- 

 ship of the two muscles is due the full, rounded appearance 

 of the posterior axillary fold. 



The latissimus dorsi is supplied by the thoracodorsal nerve. 

 It is an adductor, retractor, and medial rotator of the upper 

 extremity. 



Two Intermuscular Spaces. A triangular space mapped 

 out by the distal border of the trapezius, the proximal border of 

 the latissimus dorsi, and the base of the scapula, will now be 

 noticed (Fig. 22, p. 53). Within these limits a small portion of 

 the rhomboideus major can be seen, and also a varying amount 

 of the wall of the thorax a part corresponding to the sixth 

 intercostal space and the borders of the ribs which bound it 

 above and below. It is well to note that this is the only 

 part of the thoracic parietes on the posterior aspect of the 

 trunk which is uncovered by muscles. Further, between the 

 last rib and the crest of the ilium the anterior border of the 

 latissimus dorsi will generally be observed to overlap the 

 posterior border of the external oblique muscle of the 

 abdominal wall. Sometimes, however, a narrow triangular 

 interval exists between the two muscles, in which is seen a 

 small part of the internal oblique muscle. This space is 

 termed the trigonum lumbale (Petiti) (Fig. 17, p. 39). 



Reflection of the Trapezius. On the second day the dissector should 

 begin by reflecting the trapezius, working, if possible, in conjunction 

 with the dissector of the head and neck. Divide the muscle about two 

 inches from the spines of the vertebrae, and throw it laterally towards 

 its insertion. The trapezius is very thin at its origin, and the greatest 

 care must therefore be taken not to injure the subjacent rhomboid 

 muscles. The small bursa between the tendon of insertion of the lower 

 part of the trapezius and the triangular root of the spine of the scapula must 

 not be overlooked. 



Nerves and Vessels of Supply to the Trapezius. A dis- 

 section of the deep surface of the reflected muscle will reveal 

 the following structures : 



a. The accessory nerve. 



b. Two or three nerves from the cervical plexus. 



c. The ascending branch of the transverse cervical artery. 



These constitute the nervous and vascular supply of the 

 trapezius. 



The nerves have already been displayed by the dissector of 



