42 PRINCIPLES OF VETERINARY SCIENCE 



to the spine the infraspinous fossa. The internal surface is taken 

 up by the subscapular fossa. Above on each side are two 

 rough triangular areas for muscular attachment. The superior 

 border is thick and straight in the young and growing animal, 

 but becomes uneven with age; it gives attachment to the scapu- 

 lar cartilage. The anterior border is thin and rough in its upper 

 pait, concave and smooth below. The posterior border is thick, 

 concave, and rough. The three angles are named anterior, pos- 

 terior, and articular or humeral. The articular angle carries 

 a glenoid cavity for articulation with the head of the humerus. 



The humerus is a long bone located between the scapula above 

 and the radius and ulna below. It is directed obliquely down- 

 ward and backward. This bone has a shaft or body and two 

 extremities. The shaft is twisted in appearance and has four 

 surfaces. The external surface is marked by the musculospiral 

 groove. The internal surface is rounded from side to side and 

 presents above the middle the internal tubercle, and in its lower 

 third the medullary foramen. The anterior surface is flattened, 

 wide above and narrow below. The posterior surface is rounded 

 and smooth. The external border is the only distinct one and 

 shows a large prominence, named the deltoid tuberosity. The 

 proximal extremity is very large and somewhat four sided; it 

 presents an extremely convex head for articulation with the glenoid 

 cavity of the scapula. On each side of the head is a tuberosity; 

 in front is a subdivided bicipital groove for the play of the ten- 

 don of the biceps muscle. The distal extremity carries a pulley- 

 like surface for the bones of the forearm. Immediately above 

 and behind this articular surface is the deep olecranon fossa. 



The radius in the adult horse is united to the ulna to form what 

 appears to be one bone, but in the fetus and young animal there 

 are two distinct bones. The radius is the larger in this animal. 

 It is a long bone situated between the humerus and the carpus in 

 a nearly vertical direction, and presents for description a shaft 

 and two extremities. The shaft is curved convexly foward, 

 and has two surfaces and two borders. The anterior surface is 

 convex and smooth, while the posterior is concave in its length 

 and flattened transversely. On the external part of the pos- 

 terior surface there is a rough area for the attachment of the ulna. 

 The borders are rounded, the inner one is not covered by muscles. 

 The upper extremity carries two shallow cavities for articulation 



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