Cope.] -^"O [Dec. 2, 



tinued to Iho radial articular surface, ias'.ead of being separated by an 

 interruption as seen in the normal horse. In extensioft and flexion the 

 prominent posterior border of the new olecranar facet of the humerus 

 rotates behind tiie humeral olecranar facet just described. Posterior to 

 tin's depressed sui face there rises an abnormal bony crest which is con- 

 centric with the olecranar and humeral surfaces, and serves as a guide in 

 extension and flexion of the crest of the humerus which moves in the 

 surface in front of it, which becomes, through the presence of this crest, an 

 open groove (Ic, Figs. 4, 5). 



(3) A triangular shallow facet is formed on the posterior part of the 

 head of the radius corresponding to ihe trochlear crest of the humerus 

 (//, Figs. 2, 4). 



(4) A corresponding facet appears on the posterior part ^of the trochlear 

 crest of the humerus, which penetrates the dense layer (Ze, Fig. 1). 



(o) Tlie internal extremity of the humeral surface of the head of the 

 radius is beveled off by the expansion of the internal roller of the hu- 

 nierus, forming a new facet of perfect articular character {lb, Figs. 1, 

 3, 4). 



(G) A facet corresponding to (5) is developed on the internal roller at 

 its middle, considered either transversely or anteroposteriorly. It is of an 

 elongate oval form, and its superior portion penetrates the dense layer 

 {Id, Fig. 1). 



Class Second. (1) The trochlear groove of the head of the radius has 

 nearly closed its anterior and posterior margins by osseous outgrowths, 

 the largest of which, the posterior, so fills it as to support the external 

 part of the external humeral condyle in extension and flexion {2a, 2b, 

 Figs. 2, 4, G). 



(2) Exostoses exist on the external side of the humeral facets of the 

 olecranar process, which till jiart of the concave arc of the ulna, necessary 

 for adaptation to the external border of the humerus in its new position 

 {2c, Figs. 4, G). 



(3) At the internal and posterior sides of the head of the radius a mass 

 of exostoses causes a considerable thickening of the bone. Its thickness 

 on the internal side is just equal to the free projection of the internal 

 roller of the humerus within tlie head of the radius. It is not, however, 

 built up to the plane of the head of the radius, and so does not yet sup- 

 port the humerus. 



Summary. — As a result of the abnormal action of this luxated elbow we 

 have the following production of new structures. Four complete new 

 facetSj viz. : One on the humerus, one on the ulna, one on ulna and 

 radius, and one on the radius. Two incomplete new facets on the 

 humerus. The development of two new crests, which serve as guides to 

 rotating margins. Second, the partial filling by exostosis of two unused 

 facets, one on the ulna, and one on the radius ; third, the til ling by exos- 

 tosis of an epicondylar fossa which serves to build out a new facet; and, 

 fourth, the building out by exostosis of the head of the radius, which if 



