THE PELVIC LIMB 



muscles in any strong motion is so intricate it is not safe to state that the 

 muscular equipment is not fitted for the same swimming method as em- 

 ployed by the seal. On the other hand, there are considerable differ- 

 ences, which contribute evidence to the probability that the sea otter 

 swims by vertical oscillations of the expanded feet. In such actions 

 the muscles of the back are involved to elevate the pelvis. The erector 

 spinae is certainly fitted for this. The hypaxial muscles are not fitted 

 for depression, but the strong rectus abdominis can accomplish it, with 

 a more favorable lever arm. The lesser gluteal complex is much 



Figure 48. Lateral view of the left hind limb musculature of the desman {Des 

 fnana), redrawn from Dobson. 



Specialized for a purpose not particularly clear, for its action depends 

 upon the habitual posture of the femur and the way in which other 

 muscles co-operate. The gluteus maximus is powerful for further ex- 

 tension of the femur after it is partly extended, and the superficial 

 biceps, semitendinosus and gracilis form an extraordinarily efficient com- 

 plex for elevation of the shank when the feet are extended to the rear, 

 thus accomplishing upward thrusts oi these members. On the whole 

 the muscular details do not detract anything from the above theory of 

 the way in which this animal swims, but, on the contrary, contribute 

 considerable coroborative evidence. 



[289] 



