iS92.y 289 [Cope. 



continued would linve extended the head of the radius for adaptation 

 to the inwardly luxated humerus. 



Etiology. — That the new structures descrihcd are due to the abnor- 

 mal mechanical relations of the bones, will be questioned by no one. We 

 observe tliree distinct processes of osseous metabolism due to these con- 

 ditions. These are : Fii'st, the removal of tissue from its original locality, 

 and the substitution of dense tissue for spongy tissue at the point of 

 removal. This has been accomplished at three points. A. Where the 

 inferior extremity of the external posterior rib of the shaft of the humerus 

 has been largely cut awaJ^ in adaptation to the movement of the olecrnnar 

 crest of the ulna, and a dense layer developed over the new surface thus 

 ])r()duced. B. Where the internal border of the head of the radius has 

 been beveled oT. C. Where the' internal face of the humeral facet of the 

 olecranar process of the ulna has been planed down without exposing the 

 spongy bone. That this process was not completed at some points is 

 shown by the two new facets of the humeral condyles, where the dense 

 laj'er is penetrated and no corresponding dense layer established on the 

 spongy layer thus exposed (Figs. Id and Je). 



Secoiul. The deposit of osseous bodies beneath the sj'-novial walls where 

 the bursa was kept expanded by the fixilure of the articular ends of the 

 bones to maintain contact, as in the case of the trochlear groove of the 

 head of the radius, and the external side of the humeral facet of the ole- 

 cranar process of the ulna. 



Third. The development of exostoses at the insertions of articular lig- 

 aments and tendons at the following three points : A. At the insertion 

 of the flexor mctacarpi exlernus ligament, at the exterior border of the 

 posterior face of the inferior end of the shaft of the humerus, which crest 

 overhangs the new facet above described. B. Where the osseous crest is 

 developed on the ulna, concentric with the interior humeral facet of the 

 olecranar process. C. Where extensive exostosis appears on the internal 

 side of the head of the radius. D. Where the external cpicondj'^lar fossa 

 is filled with exostoses (other ligamentous exostoses at 3^, /and g, Figs. 1, 

 2, 4. 5). 



From the above analysis we may derive the following conclusions as to 

 the nature of the metabolism in the several cases : 



Glass First Continued excessive friction removes osseous tissue from 

 the points of contact until complete adaptation is accomplished and the 

 friction is reduced to a normal minimum. 



Class Second. Where the normal friction is wanting, and an inflamma- 

 tory condition is maintained by a pulling stress on the investing synovial 

 membrane, excess of osseous deposit is produced. 



Class Third. Stress on the articular ligaments and tendons stimulates 

 osseous deposit at their insertions, wliich deposit maj' be continued into 

 their substance. This is a pulling stress. 



CoxcLusiONS. — We find illustrated in these specimens three kinds of 

 osseous structures which are observed in normal vertebrate skeletons. 



