MECHANICS OF LOCOMOTION 



731 



lift, push, and pull forward the ponderous body. In 

 more technical terms, the straightness of the limbs 

 in graviportal animals is believed to have been 

 evolved pari passu with the short rectigrade feet and 

 with an ambling gait, while the bent or angulate 



ascertaining the position and angulation of the limbs 

 in extinct quadrupeds. The term angulation refers 

 especially to the angles which exist between the main 

 proximal and distal segments of the fore and hind 

 limbs, namely, between the humerus and ulnoradius 



I 



I 

 I 



iencion, biceps 

 to meiacarb- 



teyisor 

 fasciae 



Resultant p-ull, tendons^ 



of knee and- ankle: 



») Flexio-n: tendo femoro- 



tarseus 



Extension: tendo plautari^ 



iendo accessoritt'S 

 from biceps and 

 semitendi'^csus 



Figure 667. — Cursorial adaptation in tlie fore limb (A) and hind limb (B) of the horse 



Upper segments short, angulate, with muscle insertions at open angles (power) ; lower segments elongate, muscle 

 insertions oblique (speed) . In the standing pose the opposing flexors and extensors are stretched through 

 the weight of the animal and act more or less passively as ligaments. The equilibrium is maintained also 

 by means of special tendons on opposite sides of the limbs. After Grejory (1912.1); adapted from Schmaltz 

 (1905.1). 



character of the limbs in cursorial animals is correlated 

 with the very long, slender unguligrade feet and with 

 a rapid running, bounding, galloping, or trotting gait. 



STRAIGHTENING OF THE LIMBS AND ARCHES IN ADAP- 

 TATION TO GREAT WEIGHT (GRAVIPORTAL TYPE) 



Angulation. — The author (Osborn, 1900.181), was 

 led some years ago to study the various means of 



and between the femur and tibiofibula. All primitive 

 ambulatory and subcursorial ungulates exhibit sharp 

 angles at the elbow and at the knee which are inherited 

 from the unguiculate ancestors of ungulates. This 

 acute angle is retained in aU the cursorial and medi- 

 portal ungulates, but it tends to open out as the 

 limbs become more vertical in the graviportal digiti- 

 grades and graviportal rectigrades. 



