CHAP. iv.J THE SKELETON OF THE LIMBS. 91 



pectoral limb, and extends from the shoulder to the elbow-joint. It 

 is imperfectly cylindrical, being flattened from side to side above, 

 and from before backwards below. It describes a very slight 

 sigmoid curve from above downwards, convex forwards above and 

 concave below. 



The cylindrical part (or shaft) has its inner surface marked above 

 by a wide longitudinal depression, termed the bicipital groove, 



Fig. 52. RIGHT SCAPULA. 



A. Seen from below. 



B. Seen from within, 

 c. Coracoid process. 

 g. Glenoid surface. 



7/1. Metacroinion process. 



sb. Sub-scaptllar fossa (with two oblique ridges) 

 x. Axillary border, showing its longitudinal 



groove. 

 The acromion process is seen in figure A, just 



above the letter m. 



because it lodges the tendon of a muscle called the Biceps. External 

 to this is a slightly roughened and elevated tract (dr) called the 

 deltoid ridge, as it serves for the insertion of the deltoid muscle. 



The lower part of the shaft has its anterior surface separated 

 from the posterior surface by two lines (or ridges), one on each side, 

 which become especially well marked as they approach the lower 

 end of the bone. The outer (rs) of these two ridges (which is the 

 stronger and more posteriorly situated of the two) is termed the 

 mpinator, or external condyloid ridge, while the inner one is named 

 the internal condyloid, or pronator ridge. Just within it is an 

 elongated opening, or foramen, called i\i.Qsnpracondylar foramen (fc), 

 which transmits the median nerve and brachial artery. 



On the hinder surface of the shaft (which is generally convex) 

 there may be detected a very slightly marked oblique groove (called 

 the musciilo-spiral), passing from above downwards and outwards. 



The upper end of the humerus shows a large rounded convex 

 head (h), covered, when fresh, with cartilage, and articulated to the 

 glenoid surface of the scapula. This head is not placed on the 

 middle of the summit of the bone, but on its hinder and inner 

 aspect, so that its axis does not coincide with that of the shaft. 



On the outer and inner sides of the head of the humerus, are two 



