546 MAMMALIAN ANATOMY 



The bicipital groove (Fig. 429) is a wide and shallow excavation, 

 situated on the inner side of the front aspect of the upper extremity of 

 the humerus below the head and between the two tuberosities. It is 

 deepest and widest above, but below passes on to the internal surface 

 of the shaft. It lies at the line of meeting of the anterior part of the 

 internal surface of the greater tuberosity with the anterior surface of 

 the lesser tuberosity, the former forming its outer wall, the latter its 

 floor. The bicipital groove lodges and holds in place the tendon of 

 the biceps muscle, which is attached just above the shoulder-joint to 

 the coracoid process of the scapula. On its outer wall is inserted the 

 posterior part of the deep pectoral muscle. 



The Shaft of the humerus comprises the greater part of the bone, 

 and is the longer, slender portion between the two extremities, from, 

 which it is not sharply denned. When seen from in front, it appears 

 straight, slightly narrowed below the middle, and widening out at the 

 ends. When viewed from the side, the upper part is seen to curve 

 backward and to have an antero-posterior diameter nearly twice as 

 great as the antero-posterior diameter of the lower part. The shaft 

 is divided by anterior, internal, and external borders into internal, 

 posterior, and external surfaces. 



The anterior border (Fig. 430) begins above as the continuation of 

 the anterior border of the greater tuberosity, and runs downward, on 

 the inner side of the front of the bone, to a variable point, where it 

 fades away, permitting the external and internal surfaces to become 

 continuous in the lower third. In its upper third it is broad and 

 rounded, and is directed inward as well as downward ; it then turns 

 outward, and becomes narrower and sharper, and finally obscure. It 

 practically ends when it is joined by the lower end of the strong 

 oblique line on the external surface, called the deltoid 1 ridge, but 

 traces of it are often seen below, in one or more lines for muscular 

 insertion directed toward the inner angle of the lower extremity. On 

 the inner side of the upper half of the anterior border is inserted the 

 aponeurosis of the posterior part of the deep pectoral muscle, below 

 which the lines of insertion of the middle pectoral and the superficial 

 pectoral, which begin above on the external surface, are continued on 

 the border downward to its end. 



The external border (Fig. 428) is posterior in its upper two-thirds 



1 From delta, the Greek letter J, and eides, like. 



