40 



THE nOlt.SK IN IlEA!/rn ANl) DISEASE 



The humerus i> 

 radius and ulna ]>v 



loca.tcil 

 low. It 



ween the scapula ahovc and the 

 lirected obliciuely downward and 

 backward. This bone belongs 

 to the class of long bones and con- 

 sists of a shaft or Ijody and two 

 extremities. The shaft is twisted 

 in appearance and has four sur- 

 faces. Tlic external surface is 

 marked by the musculospiral 

 groove. The internal surface is 

 rounded from side to side and 

 presents al)ove the middle the in- 

 ternal tubercle, and in its lower 

 third the medullary foramen. 

 The anterior surface is flattened, 

 wide above and narrow l^elow. 

 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 proxi- 

 mal extremity is very large and 

 somewhat four sided ; it presents 

 a head — an extremely convex 

 articular surface for the glenoid 

 cavity of the scapula. On each 

 side of tlie head is a tuberosity; 

 in front is a subdivided bicipital 

 groove for the play of the tendon 

 of the biceps muscle. A fossa 

 is located between the head and 

 the Incipital groove, in wdiich are 

 numerous foramina. The distal 

 extremity carries a pulley-like 

 surface for the bones of the fore- 

 arm ; the internal portion of this 

 surface is larger than the exter- 

 nal (distinguishing feature). Im- 

 mediately above and back of this articular surface is the deep 

 olecranon fossa. 



Fig. 



4. — Skeleton 

 (lateral 



of left 

 view ) . 



fore limb 



