172 Dr. W. Kiikenthal on the Adaptation of 



limited number of phalanges — nine at the most — and distinctly 

 differentiated forearm, carpal, and metacarpal bones. The 

 Ichthyosauri, on the other hand, have a flipper considerably 

 further developed ; the process of the division of the finger- 

 rays into a number of small sections has led to a very great 

 hyperphalangy, in addition to which a longitudinal division 

 has set in, such as I have described for the toothed whales, 

 and both processes have undergone further development ; the 

 bones of the carpus and forearm too have decreased in size, 

 and in accordance with their simplified function have become 

 mere supporting elements. The most ancient Ichthyosauri, 

 however, show less differentiation in the skeleton of the 

 flipper*; but subsequently we find not only longitudinal 

 division of the fifth digit, but even manifold formation of 

 secondary rays at its side, with dichotomy of other fingers ; 

 thus, Ichthyosaurus longimanus, for instance, shows four rays 

 one behind the other on the ulnar side, that is nine in all, and 

 in the hand of another Ichthyosaurus we find, on tracing the 

 edge of the flipper, as many as fifteen longitudinal rays. 



The Ichthyosauri led a life precisely similar to that of the 

 whales. Thus Fraas writes t : — " In the case of Ichthyosaurus, 

 where not only the entire carpus, but also the radius 

 and ulna, have been transformed into jointless supporting 

 plates for the flipper, locomotion upon land was absolutely 

 impossible." In consequence of this their limbs were very 

 similar to those of the whales ; the flipper of the Ichthyosauri 

 also was ensheathed in a leathery skin ; as in the toothed 

 whales the fore flipper was readily bent backwards, and the 

 skeleton followed the curve. Now it seems to me probable, 

 from what has been stated, that the whale's flipper will undergo 

 a further development on the lines followed by that of the 

 Ichthyosaurs, and that the longitudinal fission of the finger of 

 the toothed whales is a process which is as yet in its infancy 

 and which, after further progressing, would finally increase 

 the resemblance to the flipper of the Ichthyosaurs. I therefore 

 regard this longitudinal fission as a new development which 

 is now taking place ; and this is a view which I have pre- 

 viously expressed. The explanation of this phenomenon 

 given by Leboucq % — " Cette tendence au dedoublement dans 

 le sens longitudinal existant dans certains doigts des ce'tace's 



* Vide Baur, " On the Morphology and Origin of the Ichthyopterygia," 

 American Naturalist, 1887, p. 840. 



t Loc. cit. p. 297. 



X Leboucq, " llecherches sur la morphologie de la main chez les 

 Mammiferes marins," Arch. Biulogie, 1889, p. 112. 



