ANTEEIOK EXTEEMITY OF VEETEBEATA. 



483 



fore-limb becomes a mere organ of support and locomotion. It is 

 clear that tliis is not a primary condition from tlie relative position 

 of the bones of the fore-arm^ which requires us to presuppose a 

 condition in which they were capable of pronation and supination. 

 As the limb ceases to have more than one function, this power is 

 lost ; the radius and ulna are connected immovably, and this may 

 lead to the atrophy of various parts of these bones, or to their more 

 complete fusion with one another. This is the case in the Ai'tio- 

 dactyla, where the distal end of the ulna is rudimentary in the 

 Ruminant forms. In the Tylopoda and Solidungula this end of the 

 uloa has quite disappeared, while the upper end is united with the 

 radius into one bone. 



The fingers may take on one of two sets of characters. In 



4 3 



Fig. 268. Skeleton of the manus of various Mammals. I Man. 71 Dog. Ill Vig. 



IV Ox. V Tapir. VI Horse. r Eadius. u Ulna, a Scaphoid, h Lunar. 



c Cuneiform, d Trapezium, e Trapezoid. / Magnum, g Uncinate, p Pisiform. 



either case the pollex is absent, and it is not functional even in the 

 digitigrade carnivora (Fig. 268, II). Of the remaining digits, 

 however, the third and fourth are so greatly developed in the 

 Artiodactyla (III IV), that the other two (2 and 5) often do not 

 touch the ground (Suina, MoschidEe). The fifth finger is next lost, 

 so that the third and fourth only are well- developed, and the second 

 forms a mere appendage (Anoplotherium). The third and fourth 

 fingers become still larger when their two metacarpals are fused 

 together (IV), while the second and fifth fingers become rudi- 

 mentary (Oxen, Sheep, Deer, etc.). The Perissodactyle series also 

 begins with the four-fingered form, but in them one finger only 

 (the third) is markedly larger (Tapir) (F). When the fifth, which 

 is already the smallest, disappears (Palteotherium), the second 

 and fourth are attached to the third in the form of appendages 



2 I 2 



