KINE TO GENESIS. 277 



become thicker, not uniformly, but in correspond- 

 ence with the periphery of the head of the humerus or 

 femur, rather than with the point of contact of the 

 latter. This point is irritated, but the contact of the 

 ball restrains osseous deposit. So it occurs that grad- 

 ually a new socket is developed, whose mechanical 

 relations correspond exactly with those of the articu- 

 lating bone. The head also acquires a strictly spher- 

 ical shape, by such contractions and atrophies as are 

 necessary to produce that result. Further, cartilage 

 appears in the place of the periosteum of the socket, 

 which functions like the primitive articular cartilage. 

 It is characteristic of both connective and periosteal 

 tissue to develop cartilage under the stimulus of con- 

 tinued friction of hard surfaces, such as occurs in dis- 

 locations and fractures." 



These observations of Hiitter have been confirmed 

 by Henke, Reyher, Moll, and Lesshaft. Henke and 

 Reyher state that the artificial prevention of flexure of 

 articulations in young dogs renders them immobile, 

 and their restraint of flexure to one direction, results 

 in a curving of the articular faces in that direction. 



I cite here two examples of modifications of struc- 

 ture under abnormal conditions which imposed new 

 impacts and strains on the parts. I have described 

 these cases, which are examples of false elbow-joints 

 in man and in the horse, in the P)-oceedings of tlie Amer- 

 ican Pliilosophical Society for 1892. 



In the first case, that of the human elbow, the 

 cubitus was luxated posteriorly, so that the humeral 

 condyles articulate with the ulna anterior to the coro- 

 noid process. The head of the radius is in contact 

 with the external epicondyle on its posterior inferior 

 face. The results are as follows. A new coronoid 



