hrdlicka] a new joint-formation 551
dergone apparently no change whatever, unless it is a very slight lengthening. This supports the probability that the bones at the time of the fracture and dislocation were those of a fully de- veloped adult. There is no indication that the humerus was in any way injured ; nevertheless, at some time after the injury, there started from the anterior border, and partly also from the external surface of the humerus, immediately above the coronoid fossa, a bony process, which grew forward, downward, and slightly outward until it exactly met the free and, as already stated, unchanged head of the radius, forming with this head not an ankylosis, but a new, free joint. The mean length of this process is 3.1 cm. ; its circumference at its middle is 3.5 cm. ; the diam- eters of the joint are antero-posteriorly 2.2 cm., and laterally 2.4 cm. The process ends in an articular socket which is 7 mm. deep in the center, but as parts of the border are broken on one side, it might have been 1 mm. deeper. The surface of the socket presents in the middle an irregular row of large vascular perforations, but outside of these it is for the greater part smooth, and there can be no doubt that it was covered with synovium. The distal two-thirds of the process are entirely free from the humerus.
We have here, in brief, then, the following conditions : The normal and apparently uninjured humerus sends out through all the parts superposed a regular new formation — a veritable pro- cess — to meet, support, and form a joint with the head of the dis- located radius almost an inch and a half distant. Such formations are no doubt extremely rare in man. I have no personal knowl- edge of anything closely similar, and I am unable to find such a case described. Regenerations of bone to which the condition in the specimen is related, are much more frequent in the lower animals than in man.
As to the exciting cause of the new process of bone, it most probably was a moderate injury of either the ligaments or the periosteum of the distal end of the humerus.
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