THE LIMBS 



159 



(Fig. 141) is saddle-shaped, permitting motion in two planes only — 

 antero-posterior and dorso- ventral. 



At the upper or proximal end of the bone, near its articular part, 

 are two more or less prominent processes for the attachment of 



Fig. 130. Seymouria (Cotylosauria). Humerus, femur, tibia. A, right humerus, <? from side, b from 

 front; B, left tibia, ventral side; C, radius; D, right femur, from behind; E; left femur, from Cacops 

 bone-bed, natural size; F, undetermined. 



muscles. That on the preaxial ventral side (Fig. 131), usually situ- 

 ated above the middle third, but often descending nearly to the 

 middle or even below the middle in stout-limbed reptiles, is the 



