240 DISSECTION OF THE UPPER LIMB. 



The aortic intercostal arteries lie with the nerves between the strata of 

 intercostal muscles, and nearer the upper than the lower rib bounding the 

 intercostal space. About the mid point of the space (from before back) 

 the artery bifurcates: one branch follows the line of the upper rib, and 

 the other descends to the lower rib ; both anastomose anteriorly with the 

 intercostal offsets of the internal mammary artery. 



A small cutaneous offset is distributed with the lateral cutaneous 

 nerve of the thorax; and other branches are furnished to the thoracic 

 wall. 



Directions. The dissector of the upper limb waits now the appointed 

 time for the examination of the thorax. But as soon as the body is turned 

 he is to take his share in the dissection of the Back, and to proceed with 

 the parts marked for him in Chapter V. 



After the Back is finished the limb is to be detached from the trunk by 

 sawing the clavicle about the middle, and cutting through the soft parts 

 connected with the scapula. 



SECTION II. 



SCAPULAR MUSCLES, VESSELS, NERVES, AND LIGAMENTS. 



Position. After the limb has been separated from the trunk it is to be 

 placed with the subscapularis uppermost. 



Dissection. The different muscles that have been traced to the scapula 

 in the dissection of the front of the thorax and the Back, are now to be 

 cleaned, and to be followed to their insertion into the bone. A small 

 part of each, about an inch in length, should be left for the purpose of 

 ascertaining the osseous attachment. 



Between the larger rhomboid muscle and the serratus magnus at the 

 base of the scapula, run the posterior scapular artery and vein, whose 

 ramifications are to be traced. 



To the borders and the angles of the scapula the following muscles are 

 connected: 



From the upper margin of the scapula arises one muscle, the omo-hyoid 

 (fig. 73, E). At its origin that muscle is about half an inch wide; it is 

 attached to the edge of the bone behind the notch, and sometimes to the 

 ligament which converts the notch into a foramen. 



The lower margin, or costa, gives origin to the long head of the triceps 

 (fig. 79, A), and to some fibres of the teres major; but these attachments 

 will be ascertained in the progress of the dissection. 



The base of the bone has many muscles inserted into it (fig. 74). Be- 

 tween the superior angle and the spine is the levator anguli scapulae, H. 

 Opposite the spine the rhomboideys minor, j, is fixed. And between the 

 spine and the inferior angle the rhomboideus major, K, is attached: the 

 upper fibres of this muscle end often in an aponeurotic arch, and are con- 

 nected indirectly to the bone by means of an expansion from it. Internal 

 to those muscles, and inserted into all the base of the scapula, is the ser- 

 ratus magnus muscle (fig. 73, D). 



On the inner surface of the upper and lower angles of the scapula the 



