DISSECTION OF THE UPPER EXTREMITY 73 



Vessels and Nerves behind the Scapula. 



Cut through the M. infraspinatus three centimetres from its 

 insertion into the tuberculum majus humeri, avoiding injury to 

 vessels beneath. Examine the bursa M. infraspinati between the 

 tendon of insertion of the muscle and the articular capsule of 

 the shoulder-joint. Reflect the main body of the muscle cau- 

 tiously backward and medialward. Cut through the M. supra- 

 spinatus in a similar way and reflect it medialward. Study 



(a) Transverse artery of scapula (A. transversa scapulae) (0. T. supra- 



scapular). 



Does it pass over or under the Lig. transversum scapulae supe- 

 rius? How is the artery distributed? Find 

 (aa) Acromial ramus (R. acromialis) going through M. trapezius 

 to rete acromiale. 



(b) Transverse vein of scapula (V. transversa scapulae). 



Of what vein is it a tributary? 



(c) Suprascapular nerve (N. suprascapularis) . 



Does it pass over or under the Lig. transversum scapulae supe- 

 rius? Review it to its origin from the supraclavicular portion of 

 the brachial plexus. Note especially the branches 



(ca) N. supraspinatus. 



(cb) N. infraspinatus. 



(d) Circumflex artery of scapula (A. circumftexa scapulae) (0. T. dor- 



salis scapulae artery). Study its exact course from origin to ter- 

 mination. Note the opportunities for anastomoses about the 

 scapula among its three main arteries 



(1) A. transversa colli. 



(2) A. transversa scapulae. 



(3) A. subscapularis. 



Since (1) and (2) come from the A. subclavia (first portion) and 

 (3) comes from the A. axillaris (third portion), the establishment 

 of a collateral circulation after ligation of the subclavian or axil- 

 lary between the origins of the arteries mentioned is seen to be 

 easily possible. 



DISSECTION OF ARM AND FOEEAEM. 



Surface Anatomy. 



The principal features were studied at the beginning of the 

 dissection. The student should now pay attention to certain 

 special points, using his own arm or that of a companion as a 

 control. 



(a) With the help of the photographs and accompanying key in Gerrish's 



Anatomy (2d edition, Figs. 971 to 979), identify the surface promi- 

 nences due to the various muscles of the arm and forearm. 



( b ) Note that the vena cephalica runs in the sulcus bicipitalis lateralis and 



the vena basilica in the sulcus bicipitalis medialis. 



