EXTRA DIGITS AND DIGITAL REDUCTIONS 343 



unto themselves the whole articular surface of the carpus and tarsus 



(D). 



Like the pig, the little water-deer (Dorcatherium) possesses four 

 distinct functional toes, but in Tragulus, a closely related form, the 

 outer toes are exceedingly slender and do not articulate proximally 

 (E). The upper ends of these small digits have been reduced in the 

 foot of the roebuck (Capreolus carca) ; in the extremities of the red 

 deer (C err us elaphus), these digits are represented only by the bones 

 of the phalanges and vestiges of the metacarpals and metatarsals (F). 

 In the foot of the sheep the outer digits are reduced to two small 

 phalanges (G) ; these are absent in the foot of the ox and the antelope. 

 Finally, the small hoofs, the only vestiges of the second and fifth digits 

 of the ox, disappear in the extremities of the giraffe and the camel (H). 



This series of extremities thus shows a reduction from five to two 

 digits. The gradual atrophy of these three toes has been ascribed to 

 the specialization of the foot as an organ of rapid locomotion. Primi- 



n. 



r/ m. 



u m. 



iv m. 



iv. m. 



w. in. 



iv in. 



H 



iv in. 



Fig. 7. A series of arterio-dactyl extremities showing successive reduction of the digits from 

 five to two. A, Ancodus (fossil); B, Hippopotamus ; C, Hyopotamus (fossil): D, Sus ; K, 

 Tragulus ; F, Cervus ; G, Ovis ; H, Camelus. 



