168 Dr. W. Kiikenthal on the Adaptation of 



showed me a manus of Manatus americanus prepared in 

 alcohol, which contained a fourth small ossified phalange in 

 the third digit, and one of Halicore dugong which contained an 

 ossified fourth phalange at the fourth and a cartilaginous 

 fourth in the third digit." 



Before this Brandt* had described a supernumerary phalanx 

 in Manatus and in Halicore, and Leboucq "j* likewise found 

 one on the third finger of the right hand of a sea-cow's skele- 

 ton. My own investigations upon this point were not 

 successful : in a manatee-foetus of 20 centim. I found, as did 

 Leboucq in his foetal Halicore, the third phalanx still com- 

 pletely cartilaginous. Ossification had proceeded very slowly ; 

 in the first and second phalanges only small round nodules of 

 bone had formed. Nor did I discover a fourth phalanx in 

 any of the numerous skeletons which I examined ; it might, 

 however, have been lost in the process of preparation. 



At my request Dr. Gadow forwarded me drawings and 

 detailed descriptions of the above-mentioned fore limbs, from 

 which it appears that in the fourth finger of the Halicore 

 there is no joint between the third phalanx and the new 

 nodule of bone, which is therefore to be regarded as a distal 

 bony germ belonging to the terminal phalanx. On the other 

 hand, there is a joint between phalanges iii. and iv. of the 

 third finger. In the same way the third finger of the hand of 

 the manatee shows no joint between phalanx iii. and the new 

 and very small bony nodule. 



It follows that we are entitled to speak of a fourth finger- 

 joint in one case only, namely in the third finger of the Hali- 

 core ; in the two other cases a joint between the third phalanx 

 and the new nodule of bone has not yet been found, and the 

 latter is nothing more than the ossification of a distal epi- 

 physis within the cartilage. 



There is no question that in the latter case we have the 

 commencement of the formation of a new phalanx. 



We have therefore established the fact that a fourth phalanx 

 does occur as a " sport " in the Sirenia. It is very small and 

 not separated from the preceding phalanx, but united with it 

 by cartilage, and can equally well be regarded as an intra- 

 cartilaginous ossified distal epiphysis of the third phalanx. 

 That a true phalanx can arise from it is shown by a case in 

 which a joint is formed between the new nodule of bone and 

 the third phalanx. 



* Brandt, " Symbols) Sirenologicse," Memoires Acad. St. Petersbourg 

 (6 C serie), Sc. Nat. t. v., 1849. 



t Leboucq, "Reckerches sur la morphologie de la main chez les 

 Mammiferes marins: Tinnipedes, Sir&iiens, Ot5tac6s," Arch. Biologie, 

 t. ix., 1889, p. 620. 



