THE HAND SKELETON OF SOME CETACEAN FOETUSES. 95 



The flippers exhibited were as follows : — 



Species. 



Approx. length 

 of foetus. 



Flippers shown. 



A. Balaenoptera physalus* (Linn.) 



B. Do. 



C. Delphinapterus (Beluga) leucas, Pall. 



21-3 cms. 



42-6 cms. 



15 cms. 



Right and Left 



do. 

 Right. 



The skeletons were exhibited by dehydrating the whole 

 nipper in absolute alcohol, and then clearing in cedar oil and 

 examining by strong transmitted light. 



Balaenoptera physalus (Linn.). 



Foetuses A. and B. show a vestigial cartilage lying between 

 the second and third digits of the well-marked series of four. 

 The condition shown in A. is very similar to that described by 

 Kukenthal from a considerably larger foetus. Foetus B. also 

 shows the vestige, but in this case only a very small nodule 

 remains. 



Kukenthal made the interesting suggestion that these 

 bodies, which in the better developed condition are distinctly 

 composed of two or three segments, are the vestiges of a digit 

 (No. 3) which has dropped out from the more generalised 

 pentadactyl hand. This suggestion was supported by a con- 

 sideration of the nerves supplying the fingers. If this inter- 

 pretation be correct, the condition is unique among mammals. 

 It is well known that in all other mammals in which there is a 

 reduction of the number of digits, the most persistent digil of 

 the series is No. 3, which may alone remain, as in the horse. 

 On this interpretation the small nodule usually considered fco 

 represent digit No. 1 must represent a prepollex. 



* This is the common " Khmer " whale, usually oalled />'. muscuhu, For 

 the alteration of the name <»n t be rules of prioril \ sec True, F. W.. Proc. I . < s '. 

 Nat. Mus. Vol. XXI, p. 621. 



