A NEW JOINT-FORMATION By ALES HRDLICKA
The specimen herein described shows in a very remarkable and beautiful way the great vis medicatrix natura. It consists of bones of the left arm and forearm, found by Mr Harlan I. Smith during his exploration of a prehistoric burial-place on the Fox farm at Mayslick, Kentucky. This exploration was conducted under the direction of the department of anthropology of the American Museum of Natural History. To the officers of the museum I am greatly indebted for the privilege of studying this interesting specimen, and for permission to publish the following description and the accompanying photographic illustration.
As will be seen from the plate (xxvii) the interest of the specimen lies mainly in the fact of a new joint-formation between the head of a dislocated radius and a bony process proceeding from the distal end of the humerus.
The genetic history of the new joint, from what we can ob- serve in the bones, is as follows : Originally there were here the three normal, and in all probability already adult, bones of the arm and the forearm. Subsequently the ulna became fractured a little above the middle. This was probably an incomplete frac- ture, and at the same time there took place a complete forward dislocation of the head of the radius, but without either this bone or the humerus being injured. Neither the fracture nor the dis- location was reduced. The broken ulna became united by a small callus. More callus bone was thrown out around the spine of the proximal segment, which was inclined to and possibly at times touched the interosseous border of the radius, and event- ually this part of the proximal segment became united to the radius by an osseous band nearly 3 cm. wide.
The head of the radius remained fully dislocated, and has un-
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