66 UNIVERSALITY OF DEGENERATIVE EVOLUTION 



This results in the degeneration of all the 



muscles which caused this mobility in their 



terrestrial ancestors. 



A similar degeneration may be observed among 



Plesiosaurians, Ichthyosaurians, and Mosasaurians. 1 

 With regard to Sirenia, the Dugong is unable to 

 move the arm at the elbow 

 joint, but the Manatee can 

 grasp things with its fins. 

 Besides many other modifi- 

 cations, the adaptation of 

 these animals to an aquatic 

 life has entailed the fusion 

 of the two bones of the fore- 

 arm, thus involving the de- 

 generation of those muscles 

 which formerly prevailed 

 over the movement of the 



europaea (the Mole). hrmp wViPn 



R, radius; s, scaphoid; e, semi- *> wo ' wn( 



lunar ; c, cuneiform; j>, pisiform; 7 Adnntnttrvn in 



Cuneiform; m, os magnum; ' Adaptation tO 



%. There are two types 

 of adaptation to burrowing 

 that of the Mole and 



that of the Heterocephalus. 



In the mole (fig. 35), the fore-limb, although it 



has become shorter in order that it may better fulfil 



1 L. Dollo, Premiere note sur les Mosasauriens de Mesvin (Bull. 

 Soc. belg. Gtol. Paldont. Hydrol., vol. iii., 1889) ; Nouvelle note 

 sur I'ost^ologie de Mosasauriens (Bull. Soc. belg. Gfol. Pal&nt, 

 Hydrol., vol. v., 1892). 



Taipa 





