THE HUMERUS 



77 



Tubn-osity 



Coracoid 

 process 



externally; just above its postero-external part is a tubercle to which a tendon of 

 the teres minor is attached. The bicipital tuberosity or tuber scapulae is the 

 large rough prominence in front, to which the tendon of origin of the biceps brachii 

 is attached; projecting from its inner side is the small coracoid process (Processus 

 coracoideus), from which the coraco-brachiahs muscle arises. 



Development. — The scapula has four centers of ossification, viz., one each 

 for the body of the bone, the Ijicipital and cora- 

 coid processes, the anterior part of the glenoid 

 cavity, and the tuber spina?. The last ossifies 

 after birth and fuses Avith the spine about the 

 third year. The bicipital tuberosity and coracoid 

 fuse with the body of the bone about the end of 

 the first year. 



In old subjects the spongy substance disappears at the 

 middle part of the fossie, so that the bone consists here of 

 a thin layer of compact substance. Considerable ossifica- 

 tion of the cartilage is usual, the borders become much 

 rougher, the muscular lines are more pronounced, and a 

 medullary cavity may appear in the neck. Much varia- 

 tion occurs in dimensions and slope. The average ratio 

 between the length and breadth (scapular index) is about 

 1 : 0.5, but in many cases the base is relatively wider. 

 The inclination on a horizontal plane varies from fiO to 65 

 degrees. Exceptionally the coracoid process reaches a 



length of an inch or more {2^4 to 3 cm.), and the chief nutrient foramen may be on the pos 

 terior border or in the subscapular fossa. 



Fig. 43. — Distat. End of Left Scapula 

 OF Horse, End View. (After 

 Schmaltz, Atlas d. Anat. d. 

 Pferdes.) 



THE HUMERUS 

 The humerus is a long bone which extends from the shoulder above, where it 

 articulates with the scapula, to the elbow below and behind, where it articulates 

 with the radius and ulna. It is directed obliquely downward and backward, form- 



Internal 

 tuberosity 



Posterior part 



Anterior part 



Posterior part 



J. External 

 I tuberosity 



Anterior part j 



Bicipital groove 

 Fig. 44. — Proximal End of Left Humeru.s of Horse, End View. (After Schmaltz, Atlas d. Anat. d. Pferdes.) 



ing an angle of about 55 degrees with a horizontal plane. It may be divided into a 

 shaft and two extremities. 



The shaft or body (Corpus humeri) is irregularly cylindrical and has a twisted 

 appearance. It may be regarded as having four surfaces. The external surface 

 is smooth and is spirally curved, forming the musculo-spiral groove (Sulcus musculi 

 brachialis) , which contains the brachialis muscle ; the groove is continuous with the 

 posterior surface above and winds around toward the front below. The internal 

 surface is nearly straight in its length, rounded from side to side, and blends with 

 the anterior and posterior surfaces. Just above its middle is the internal or teres 



