PART SECOND. 



ANATOMY OF THE UPPER EXTREMITY, 

 THORAX, AND BACK. 



. DISSECTION I. 



PECTORAL AND DELTOID REGION. 



A large block is to be placed under the subject so that the scapulae 

 shall rest upon it; the arm should extend at an obtuse angle with the 

 body; the dissector stands upon its inner side. An incision is to be 

 made, commencing at the third rib (a longitudinal incision along the 

 median line of the sternum is supposed to have been already made, 

 when the subject was injected), and continued in a straight line to 

 about the middle of the arm. The two flaps of skin thus marked 

 out, with the fat and cellular tissue beneath, are then to be suc- 

 cessively reflected upward to the clavicle, and downward to the limits 

 of the origin of the pectoralis major. This dissection brings the fol- 

 lowing parts into view : 



The PECTORALIS MAJOR MUSCLE arises from the sternal 

 half of the clavicle, half of the sternum in its whole 

 length, the cartilages of all the true ribs, except the last, 

 and from the aponeurosis of the external oblique muscle 

 of the abdomen ; from which a muscular slip is occasion- 

 ally added, which slip may continue separately from the 

 pectoralis, and have a distinct insertion into the humerus. 

 From this origin the fibres converge to form a flat tendon, 

 inserted into the external ridge of the bicipital groove of 

 the humerus, with this peculiarity, viz: that the fibres 

 are rolled upon themselves, in such a way that those of 

 the upper portion of the muscle are inserted into the lower 

 part of the ridge, and those of the lower portion into the 

 upper part. That part of the muscle arising from the 

 clavicle is separated from that arising from the sternum 

 by a cellu)a iiitefsp&ce, tlie^ize of wfriQh,, as well as the 

 extent of fctiv&Qp' qecjjpiecl -by t'tie' stqrnyJ .origin, varies 

 acco 

 ciation 



nt of fctivQp' qecjpiecl -by ttie stqrnyJ .origin, varies 

 rding tp tjie muscular development, or degree of ema- 

 ion I/resent ''I, by ivu-h iml'viciual subject. Near the 



