170 Dr. W. Kiikentlial on the Adaptation of 



Delphinus detyht's, where the ossified secondary epiphyses are 

 completely separated from the secondary phalanx ; I find the 

 same thing in Tursiops tursio and Lagenorhynchus albirostris. 

 This process of the formation of tertiary phalanges, which is 

 now progressing, will arrive at completion when the secondary 

 phalanges and the secondary epiphyses shall have attained an 

 equal size; and this will ensue from the progressive retarda- 

 tion of the ossification. 



Now, since from the skeletogenous tissue of the fingers in 

 the one case the three phalanges of the typical Mammalian 

 hand are preformed in cartilage, while in the other there 

 results the formation of a number of cartilaginous pieces, the 

 term " phalanx " will gradually lose its meaning for the 

 latter. Functions become simplified more and more, and the 

 finger is built up from a series of small skeletal elements, 

 which are only partially ossified. A distinction of function 

 is perceptible only in so far as the fifth finger of many toothed 

 whales is utilized to an increased extent as a supporting 

 organ. The flipper of the toothed whales is in fact more or 

 less inflected on this side, and the fifth digit has to undertake 

 the task of supporting the expanse of surface which results 

 from the inflexion. We therefore also see how the fifth finger 

 materially exceeds the others in breadth. In consequence of 

 the retarded ossification, which we have established as a 

 process of perfectly general occurrence in the Cetacean flipper, 

 the bony nuclei will no longer suffice for the support of an 

 entire pseudo-phalanx ; and we therefore find that they have 

 a lateral origin, and leave a broad cartilaginous mass on the 

 outer side of each phalanx. A further consequence of the 

 great increase in the breadth of the finger is that the separa- 

 tion of the several finger-joints is no longer complete ; the 

 dividing groove no longer extends across the entire breadth 

 of the finger, but there ensues a bifurcation on both sides, so 

 that a new cartilaginous piece is detached. With this there 

 commences that splitting-off process, which finally leads to a 

 longitudinal division of the finger. The split-off portions of 

 the newly-formed series now receive bony nuclei on their own 

 account. This splitting-process, authenticated by me in the 

 case of several whales and confirmed by Leboucq, is particu- 

 larly well seen in certain individuals of the white whale, 

 where I have described it both in the adult and in a small 

 embryo *. Thus the process of the formation of small skeletal 

 parts proceeds, in this case also hand in hand with retarded 

 ossification. 



* Kiikenthal, " Ueber die Hand der Cetaceen," 1 und 2 Mittheilung-, 

 Anat. Anzeiger, 1888, nos. 22 and 30. 



