544 MAMMALIAN ANATOMY 



The head of the humerus presents behind (Fig. 431), below the 

 jagged line which limits the articular surface, external and internal 

 surfaces lying between the upper ends of the internal border and the 

 deltoid ridge and separated by a ridge which is the beginning of the 

 posterior border of the bone. These surfaces are excavated, rough- 

 ened, and pierced by venous foramina. They are continuous with the 

 posterior and external surfaces of the shaft, and give origin to the 

 upper part of the posterior humeral head of the triceps muscle. 



The greater tuberosity (Figs. 427, 428) is a broad, flattened pro- 

 cess applied to the front of the outer side of the head in such manner 

 that the narrow upper edge projects above the articular surface, and 

 the external surface faces outward and forward. 



The superior border is a rounded convex crest which begins behind 

 as a line at the upper end of the deltoid ridge. It widens gradually 

 as it arches upward, and then, becoming more flattened and facing- 

 inward, curves down to the front ; here, at a roughened swelling, it 

 changes slightly its direction, and, becoming a rounded anterior border, 

 passes straight down into the anterior border of the shaft. 



The internal surface of the greater tuberosity (Fig. 427) is pointed 

 above and behind, and wide below. At first it forms the anterior 

 external wall of the articular surface of the head and faces inward and 

 backward, but lower down it becomes wider and rougher, faces almost 

 directly inward as the outer wall of the bicipital groove, and is con- 

 tinuous below with the inner surface of the shaft. 



The superior and anterior borders and the edges of the adjoining 

 surfaces of the greater tuberosity give insertion to the supraspinatus 

 muscle, and the internal surface, near the articular surface and the 

 bicipital groove, to the anterior part of the deep pectoral and the 

 upper portion of its posterior part. 



The external surface of the greater tuberosity is bounded above by 

 the arcuate superior border, in front by the arcuate anterior border, 

 and behind by the sharp emarginate beginning of the deltoid ridge. 

 It passes below, without change of direction, into the external surface 

 of the shaft ; in the bone of a young specimen its lower limit is often 

 seen as an arched line more or less distinct crossing the surface and 

 indicating the point of union of the epiphysis with the shaft. The 

 surface is divided into anterior and posterior parts by a roughened 

 line which begins behind the middle of the upper margin and runs 



