DISSOROPHUS COPE 531 



probable. As to its fate, the only theory suggested is that of Gaudry, 

 that it represents the acromial ossification of the higher vertebrates; 

 and this too seems not unreasonable. The union between clavicle and 

 cleithrum in Dissorophus is a very close, sutural one; in the early 

 reptiles only the lower end of the cleithrum is left; the co-ossification 

 of this with the scapula would account for the acromion, if it be not a 

 mere epiphysial ossification. In Eryops the cleithrum is suturally 

 united throughout with the scapula above, in the position of the supra- 

 scapula. 



Interdavicle. — The interclavicle is a broad, gently concave, and 

 thin bone, resembling that of Cacops, but larger and broader. It has 

 a rounded, thin border anteriorly, and similarly rounded, thin lateral 

 margins. Posteriorly the bone is broken away but the thickened 

 median part indicates a posterior median extension, probably as in 

 Cacops. 



Clavicles. — The clavicles are large, broad, smooth bones, meeting 

 each other in the middle line, and covering, for the most part, the 

 interclavicle. They are convex below, with their greatest expansion 

 some distance away from the middle. In the position in which the 

 girdle now is, evidently the normal one, the cleithral ends are directed 

 vertically upward, nearly parallel to each other, with an interval of a 

 little more than two and a half inches between their upper extremities, 

 which are suturally and closely united to the lower ends of the cleithra 

 or supraclavicles. The upper extremity is much stouter and broader 

 than is the case with Cacops. 



Upon the whole, the pectoral girdle, both primary and secondary, 

 is remarkable for its stoutness and firm articulations. 



Humerus. — Of the two humeri, the left is preserved completely 

 save the capitellar angle, while the right has the lower end perfect with 

 the upper extremity wanting. In the figures the capitellar portion has 

 been reversed from the right side. In general shape and structure the 

 bone resembles that of Cacops closely, so closely that there may be 

 difficulty in distinguishing them in ill-preserved specimens. The 

 humerus of Dissorophus is distinctly stouter, with the ends a little 

 more expanded and the lateral curvatures a little deeper; the entepi- 

 condylar expansion is stouter. 



Femur. — ^The right femur is preserved in pretty good condition 



