PROGRESSION ON THE LAND. 



Walking of the Quadruped, Biped^ etc. — As the earth, because 

 of its solidity, will bear any amount of pressure to which it 

 may be subjected, the size, shape, and weight of animals 

 destined to traverse its surface are matters of little or no 

 consequence. As, moreover, the surface trod upon is rigid 

 or unyielding, the extremities of quadrupeds are, as a rule, 

 terminated by small feet. Eig. 18 (contrast with fig. 17). 



Fig. 18.— Chillingham Bull (Bos Scoticus). Shows ppwerfnl heavy body, and 

 the small extremities adapted for land transit. Also the figure-of-8 move- 

 ments made by the feet and limbs in walking and running, ii, t Curves 

 made by right and left anterior extremities, r, s Curves made by right 

 and left posterior extremities. The right fore and the left hind f(^ot move 

 together to form the waved line (s, v) ; the left fore and the right hind foot 

 move together to form the waved line (r, t). The curves formed by the 

 anterior (U y) and posterior (r, s) extremities form ellipses. Compare with 

 fig. 19, p. S9.— Original. 



In this there is a double purpose — the limited area pre- 

 sented to the ground affording the animal sufficient support 

 and leverage, and enabling it to disentangle its feet Avith tlie 



