730 



TIT.^><'OTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



FiGUEE 666.- 



-Cursorial adaptation for the trot, run, and gallop in the horse (Ai-Aj) ; graviportal adaptation for 

 the walk and amble in the elephant (Bi-B,). After Gregory, 1912.1 



Ai, The gallop of a horse, showing the leaping, catapult action of the slender limbs in a cursorial type. 



Bi, The amble of an elephant, showing the steady sweep and great weight-lifting power of the ponderous limbs in a graviportal type. 



As, B2, Extremes of cursorial adaptation in a Miocene horse, Hipparion (Neohipparion) (A2), and of graviportal adaptation in a mastodon (Bs). 



A3, B3, Angulation of limb segments and muscles in a horse (A3) and a mastodon (B3): 



Cursorial (A3) 

 Hium and femur ar right angles in the standing pose. 

 Muscles inserted at open angles, giving great propulsive power. 



Head of femur low, at right angles to shaft. 

 Longissimus dorsi works in tandem with gluteus medius. 



Graviportal (Bj) 



Ilium and femur more nearly vertical. 



Muscles inserted at more acute angles, giving great vertical or weight- 

 lifting power. 



Head of femur high, at top of shaft. 



Longissimus dorsi cut off from gluteus medius. 

 Cmrsorial hind foot (Hipparion, Neohipparion), for springing and rapid lifting. B4, Graviportal hind foot (Mastodon), for powerful, slow 

 lilting. Fulcrum at B', b'; power at B, b; resistance at A, a. If the pull of the calf muscles (M,m) and the weight at the ankle joints (W,w) 

 were respectively equal, the long, cursorial foot would have great "moment of resistance" (WXB'A) and small "moment of power" (MXBB'), 

 with high speed; whereas the short, graviportal foot would have relatively small moment of resistance (wXba) and great moment of power 

 (mX&60, with slow speed. 



