VERTEBRATA : MAMMALIA. 



645 



Normally each digit has three phalanges, except the thumb, 

 which has only two. In the Whales and Dolphins (Cetacea), 

 in which the anterior limbs form swimming-paddles, very like 



Fig. 354. A, Fore-leg of Ox (Bos taurus). B, 

 Hind-leg of Stag (Cervus elaphus). ca Carpus ; 

 ta Tarsus; c "Canon-bone," composed of the 

 united metacarpals or metatarsals of the 3d 

 and 4th digits. 



Fig. 355. Fore-leg of Horse. 

 ca Carpus; m Metacarpal 

 of the third digit ; s " Splint- 

 bone," or rudimentary met- 

 acarpal ; i, First phalanx 

 or "great pastern;" 2, 

 Second phalanx or " small 

 pastern ; " 3, Third phalanx 

 or "coffin-bone." 





those of the Ichthyosaurus and Plesiosaurus, the phalanges are 

 considerably increased in number as they are in those Reptiles. 

 In all the Mammalia, too, except the Cetacea, it is the rule 

 that the terminal phalanx in each digit should carry a nail, 

 claw, or hoof. 



