1892.] ^ 280 [Cope. 



ported by the external bones of the carpal and tarsal series respectivel}'. 

 The reduction of the external digit deprives the external bones in question 

 of their share in the support of the general weight, and consequently relieves 

 them of impact, which now passes through the longer median digits which 

 remain. The median digits, on the other hand, support the radius and tibia 

 through the medium of the carpus and tarsus, and it is these elements, 

 therefore, which function in the use of the limb. We have here an evident 

 illustration of the effect of disuse in effecting the atrophy of an element, 

 and of use in increasing the size and complexity of an adjacent element of 

 the same organism. No other explanation seems possible, for the ele- 

 ments which are reduced and those which are enlarged are subjected in 

 every other respect to the same conditions. 



On False Elbow Joints. 



By Prof. E. D. Cope, Ph.D. 



{Read before tlie American Philosophical Society, December 2, 1S92.) 



I have in various papers formulated and defended the hypothesis that 

 the peculiar characters of the articulations of the mammalian skeleton are 

 due to mechanical causes operating throughout the ages of geologic time.* 

 I had previously traced the succession of these modifications from simple 

 reptilian types, through various stages, to the highly specialized and 

 mechanically perfect structures seen in the higher Mammalia. The 

 series of forms revealed by paleontologic research is so complete as to leave 

 little doubt in the mind as to the manner and cause of their origin. The 

 theory thus derived, which I have called kinetogenesis, depends for its 

 demonstration on two assumptions. The first is that living osseous tissue 

 is plastic, and is therefore readily modified in its form by impacts, strains, 

 friction, etc. ; and the other is that one which is necessary to all evolu- 

 tionary hypotheses, that acquired characters are inherited. I do not pro- 

 pose to discuss here the latter proposition, but I desire to offer some 

 evidence in support of the former. Marey tells up,f as a result of a study 

 of pathological conditions of articulations, that "after dislocations the old 

 articular cavities will be filled up and disappear, whUe at the new point 

 where the head of the bone is actually placed, a fresh articulation 

 is formed, to which nothing^ will be wanting in the course of a lew 

 months ; neither articular cartilages, synovial fluid, nor the ligaments 

 which retain the bone in place." 



Specimens demonstrating the truth of this statement of Maiey are also 



* Origin of the FMcst, 1887, p 368 el seq. ; " The IMcchanical Origin of tlie Hard Parts of 

 the Mammalia." American Journal of Morphology, ISSO, p. H8. 

 t Animal Mechanism, 1874, pp. 88, 89. 



PKOC. AMEll. PHILOS. SOC. XX.^. 139. 3k. PUIXTED JAN. G, 1893. 



