THE PECTORAL LIMB 



would be the case in mammals. Furthermore, in spite of the fact that 

 hyperyhalangy is much more marked in some whales than others, and 

 even in some digits of a particular individual than in other digits, all 

 phalanges are perfectly and uniformly graduated in decreasing size distad 

 from the carpus. . If the supernumerary phalanges had intercalary origin 

 of this sort it is, to my mind, entirely inconceivable that all of these 

 added elements could now invariably occur in perfect and complete de- 

 velopment, being indistinguishable from the true phalanges. Rather 

 would there frequently be encountered a number of elements throughout 

 one -particular phalangeal series, at least in some whales, which were 

 markedly smaller and different in shape from the true phalanges. Fi- 

 nally, what appears to render the theory incontrovertibly untenable 

 insofar as concerns Cetacea is the virtual certainty that were it a fact 

 there would be embryological evidence to support it. In the first place 

 there would, during embryonic development of the arm, likely be a 

 stage by no means short during which the intercalary elements would be 

 relatively much smaller than the phalangeal ones. In the second and 

 this is the most important point of all had any of the phalanges ever 

 had origin by intercalary syndesmosis, the cartilage in which they are pre- 

 formed would have to be fibro -cartilage, while that of the true phalanges 

 would be hyaline cartilage: but all of them are uniformly hyaline. 



(4) Kukenthal argued with his customary ingenuity that hyper- 

 phalangy in the Cetacea is attained by means of the separation and sub- 

 sequent development of the phalangeal epiphyses. According to this 

 theory, then, the retardation of the ossification of the phalangeal shafts 

 allowed greater individuality of the epiphyses, and these, lacking the 

 stimulus for conservativeness usually imposed by synovial joints, were 

 permitted to increase in size, following a trend toward longer digits, until 

 they had attained the exact conformation of the phalangeal shafts. The 

 facts that this process could account for but eleven or twelve phalanges, 

 and that the proximal ones still show double epiphyses did not deter the 

 sponsor of this theory in the slightest; nay, it but stimulated him to 

 claim that after this had once taken place, it occurred all over again a 

 second time, or a third if necessary, giving birth to as many elements as 

 needed. Unlike Zeus, however, these epiphyses could not spring forth 

 full panoplied, as perfect phalanges, and if they had such origin there 

 would surely be encountered various stages in their development, so 

 that in a single digit of at least some whales there would not be a uni- 

 form diminution in all the phalanges, but some would be abruptly smaller 

 than their neighbors, while some phalangeal shafts would have epiphyses 



[263] 



