278 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



process was developed in front of the abnormal posi- 

 tion of the humeral condyle to an elevation above the 

 shaft of the ulna exceeding that of the normal coro- 

 noid. Between it and the normal coronoid was devel- 

 oped a perfectly functional cotylus which embraces 

 the humeral condyle like the normal cotylus. The 

 latter has its articular surface, buried under osseous 

 deposit, so as to be no longer visible. The region of 

 contact between the head of the radius and the external 

 epicondyles, has developed in the latter a large artic- 

 ular cotylus which permits of both rotary and ver- 

 tical movement of the former. The articular surface 

 of the humeral condyles, except where in articulation 

 with the ulna, is roughened, and partially overgrown 

 with exostoses, so as to alter its form to a great extent. 

 The opportunity of examining this specimen I owe to 

 Provost Pepper of the University of Pennsylvania, in 

 whose museum it is preserved. 



In the case of the horse's elbow, the luxation of 

 the cubitus is inward, so that the olecranon articulates 

 with the external epicondylar surface, and the humeral 

 condyles are not adapted to the head of the radius ; 

 their internal border falling considerably internal to 

 the inner border of the radius. The horse from which 

 this specimen was derived lived for two years after the 

 luxation took place, and became able to use the limb 

 in some degree. The effect on the articulation is as 

 follows. 



A large part of the inferior extremity of the poste- 

 rior rib of the shaft of the humerus, which is the place 

 of insertion of the external flexor nietacarpi muscle, has 

 been removed, so as to present a wedge-shaped out- 

 line with the apex downward. This removal permits 

 the close articulation of the inner face of the olecranal 



