166 Dr. W. Kiikenthal on the Adaptation of 



If we examine the extent to which this phenomenon occurs 

 in the fore limbs of each of the aquatic mammals which I 

 have enumerated, we shall find that the skeleton of the manus 

 has undergone least modification in those animals which 

 exhibit least material modifications in other i-espects also, the 

 only noticeable change being that the epiphyses become larger 

 and more distinct. 



In Bydromys chrysogaster and Hydrochcerus capybara the 

 ossification is slightly more tardy, and we already perceive 

 indications of double epiphyses, just as in the metacarpals of 

 Omithorhynchus ; in the case of the otter it has already been 

 remarked by Allen Thomson * that " the ossific union of the 

 epiphyses in these animals seems to be comparatively tardy." 

 In the case of the beaver this is equally true. We have 

 therefore a whole series of transitions between hands with one 

 epiphysis and those with two epiphyses on each finger-joint. 

 As for the seals, it has been stated by Weber f : — " In the 

 Pinnipedia the ossification of the hand takes place on the 

 usual plan, in that proximal epiphyses only are developed ; 

 in the foot, however, all the phalanges, with the exception of 

 the last, have a distal epiphysis in addition to the usual 

 proximal one." This assertion is not strictly accurate ; it 

 has already been stated by Flower, in his ' Osteology of the 

 Mammalia,' \ that Macrorhinus leoninus has double epiphyses 

 in the hand, a discovery which I was myself able to confirm. 

 I found double epiphyses in hand and foot in the following 

 Pinnipedes — Macrorhinus leoninus, Stetiorhynchus leptonyx, 

 Otaria jubata, and Arctocephalus cinereus ; indications in 

 Trichechus rosmarus] in the foot only in Cystophora cristata. 



In the Sirenians, too, I have the same state of things to 

 report. That ossification takes place tardily in these animals 

 also I found from examination of the hand of an embryo 20 

 centim. in length, in which the terminal phalanges were still 

 cartilaginous, while in the remainder the diaphyses were 

 visible as small round nodules. The consequence of this is 

 that in the adult there is a tendency towards the formation of 

 double epiphyses. 



Thus in Manatus senegalensis the distal epiphyses of the 

 metacarpals are frequently separate ossifications, while in 

 Ualicore dugong double epiphyses, which ossify later and are 

 completely separated, are found. 



* Allen Thomson, " On the Difference in the Mode of Ossification of the 

 First and other Metacarpal and Metatarsal Bones," Journ. Anat. & Phys. 

 1869, p. 131. 



t Weber, ' Studien an Saugethieren,' p. 170. 



\ Flower, ' Osteology of Mammalia,' 1885, p. 347. 



