Mammals to Aquatic Life. 169 



That which is only commencing to take place in the 

 Sirenia and is found as a rare variation has already been con- 

 summated in the whales, and is of quite general occurrence. 

 The original different morphological value of the several 

 secondary phalanges is no longer embryologically visible ; 

 but, on the contrary, diaphyses and epiphyses are separated 

 and arise as equivalent pieces of cartilage, while simple 

 symphyses have been formed in place of the joints. 



The process of separate epiphysis-formation in the manus 

 of the whale appears to have undergone a further development 

 in a proximal direction. The wrist-bones, which ossify very 

 late, are indeed affected less, or even not at all, though it is 

 stated by Flower * that in the cachalot there exists a species 

 of epiphysis-ossification in the carpus, there being a central 

 nucleus and a peripheral fringe of bone. Much more frequent 

 are the cases in which the radius and ulna form large double 

 epiphyses, the bony centres of which may remain separate. I 

 have already, in the case of an advanced embryo of Phoccena 

 communis^, drawn attention to the manner in which it is possible 

 for new skeletal parts to arise owing to this retarded ossifica- 

 tion of the epiphyses, and I am now able to allude to the 

 hand of an adult whale \ } Hyperoodon rostratus, in which the 

 double epiphyses of the radius and ulna have developed into 

 independent skeletal elements, with their own bony centres. 

 The tendency towards a formation of epiphyses in the bony 

 parts of the fore arm is already commencing anew, in that a 

 narrow border next to the old epiphysis is incompletely 

 ossified. 



We have thus seen how the process of the formation of 

 small skeletal parts, which has long found expression in the 

 case of the fingers, is commencing in the bones of the fore 

 arm also, and that therefore the process is not standing still. 

 We find a further proof of this in the occurrence of double 

 epiphyses on the secondary phalanges. In this case also is 

 retarded ossification the cause of their formation. These 

 secondary double epiphyses, again, may now ossify on their 

 own account, and with this there commences the formation of 

 tertiary phalanges. This process is beginning to take place 

 in certain toothed whales only. Thus I find it in a hand of 



* Flower, " On the Osteology of the Sperm Whale," Trans. Zool. Soc. 

 London, vol. vi. 



t Kukenthal, " Ueber die Hand der Cetaceen (dritte Mittheilung)," 

 Anat. Anzeiger, 1890, no. 2. 



\ Preserved in the museum of the College of Surgeons, London, the 

 Cetacean material of which institution was most readily placed at my 

 disposition by Prof. Stewart. 



Ann. & Mag. N. Hist. Ser. 6. Vol. vii. 12 



