2 8 2 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



adaptation is accomplished and the friction is reduced 

 to a normal minimum. Then a normal articular sur- 

 face is produced. 



Second. Where the normal friction is wanting, 

 and an inflammatory condition is maintained by a pull- 

 ing stress on the investing synovial membrane, excess 

 of osseous deposit is produced. 



Third. Stress on the articular ligaments and ten- 

 dons stimulates osseous deposit at their insertions, 

 which deposit may be continued into their substance. 

 This is a pulling stress. 



These observations therefore show that osseous de- 

 posit is produced by different forms of mechanical 

 stimulus. 



EXPLANATION OF FIGURES 66 AND 67. 



1-5, Homo sapiens, luxated elbow joint (one-half natural size); i, luxated 

 elbow joint, from within ; 2, luxated elbow joint, from outer side ; 3, humerus, 

 posterior view of distal region ; 4, humerus, distal view ; 5, ulna and radius, 

 anterior (superior) view ; 6-11, bones of abnormal left elbow joint of horse 

 (one-half natural size) ; 12, 13, normal bones of elbow joint of horse (one-half 

 natural size); 6-12, humerus, distal views; 7-13, cubitus, proximal views; 8, 

 humerus, external view of distal extremity; 9, humeral articulation of cubi- 

 tus, from above; 10, cubitus, internal view ; n, cubitus, external view. Let- 

 tering. H, humerus ; U, ulna ; fi, radius ; C, coronoid process ; Cz, second 

 (abnormal) coronoid process; O, olecranon ; En, entepicondyle ; EC, ectepi- 

 condyle ; Eno, entepicondylar exostosis ; Eco, ectepicondylar exostosis ; Co, 

 condylar exostosis ; Cos, superior condylar exostosis ; Cot, inferior condylar 

 exostosis; Hf, humeral facet ; Rf, radial facet ; Uf, ulnar facet; Op, olecranar 

 process of ulna ; Cp, coronoid process of ulna; Og, olecranar groove of hu- 

 merus; Tc, trochlear crest of humerus; Tg, trochlear groove of humerus; 

 Ehc, external humeral facet of coronoid process; Ike, internal humeral facet 

 of coronoid process; za, abnormal facet for coronoid process of ulna; ib, 

 do. for internal roller of humerus; ic, do. for abnormal facet of humerus; 

 id, do. for internal border of radius; ic, do. for olecranar process of ulna ; 

 if, do. for trochlear crest of humerus ; 2a, 2b, 2c, exostoses of radius and ulna 

 to fill vacuity between humerus and radius and ulna, ja, abnormal crest 

 which serves as a guide to the olecranar process of the humerus ; J&, abnormal 

 crest which serves as a guide to abnormal crest ja ; jc, exostosis extending 

 head of radius inwards to equalize its width with inward luxation of humerus ; 

 3d, exostoses of external epicondyle of humerus, to equalize its width with 

 outward luxation of radius; je, abnormal exostosis of insertion of external 

 flexor metacarpi muscle ; 3f, 3g, abnormal crest at insertion of external ar- 

 ticular ligament on olecranar process of ulna. 



