2 THE AMKR/C.LY .V.17rA\l/./.s/: [\< u. .WW 1 1 I. 



occurs among predaceous mammals such as the carnivorous mar- 

 supials and the true Carnivora, while defensive flight is found 

 among herbivorous forms both among the marsupials and in the 

 placental orders Rodentia, Perissodactyla, and Artiodactyla. 



Fce't and Limbs : — The main foot adaptations are shown in 

 the passage from a primitive plantigrade to a digitigrade or to 

 an unguligrade condition, and in the reduction of the number 

 of digits ; the last being often accompanied by a close apposition 

 or even by a fusion of the remaining bones of the metacarpus or 

 metatarsus, and a reduction of the number of bones in the wrist 

 and ankle. Cursorial adaptation leads to the formation of true 

 ginglymoid joints in the carpus and tarsus, the motion being lim- 

 ited to flexion and extension though the angle of movement is 

 increased. This motion is confined to the proximal podials, while 

 the distal ones become flat and may either fuse with each other 

 as in the Pecora, or with the metapodials as in the Tragulid^e. 

 The development of tongue and groove joints mars the efficiency 

 of the limb for other purposes than running. 



The laws which govern digital reduction among vertebrates 

 lead to an interesting grouping of the Mammalia with the 

 Amphibia in which the order of reduction is first digit I then 

 digit V as contrasted with the Sauropsida, the reptiles and birds 

 in which the fifth digit is invariably the first to disappear, fol- 

 lowed by digit I. 



The axis of the mammalian foot may lie in digit III as in the 

 perissodactyls and in most rodents though not in the Lepo- 

 ridse ; between digits III and IV as in the Artiodactyla and Car- 

 nivora, or in digit IV as in the diprotodont marsupials. 



Another marked cursorial adaptation is the increase in length 

 of the lower leg and foot both absolutely and in relation to the 

 length of the femur ; the lengthening of the limb increases the 

 stride while the raising of its centre of gravity quickens the 

 motion. This modification reaches its highest expression in 

 creatures of moderate size such as the medium sized antelopes 

 for in larger animals the increase in weight demands greater 

 structural strength which limits the degree of such elongation. 



The Carnivora whose need of cursorial adaptation, outweighed 

 by a greater need of varied motion, is less than that of other 



