THE PELVIC LIMB 



I am unable to discuss Limnogale with any profit for I have never 

 seen a specimen and have been able to find nothing of significance 

 in the literature save that the toes are webbed and the distal part only 

 of its powerful tail is laterally compressed. Potomogale, the insecti- 

 vore otter (fig. 4) is peculiar in that there is no present evidence that 

 the hind feet were ever used for efficient aquatic propulsion, for the legs 

 are short and the toes unwebbed. In the case of other aquatic insecti- 

 vores, as well as rodents, the feet are used for swimming pending the 

 modification of an adequate tail, which is theoretically the more efficient 

 propulsive organ, and during this time the former are confidently ex- 

 pected to become quite notably altered. Hence it is requisite to assume 

 that even from the first this insectivore had a phenomenally powerful 

 tail, robust at base, and consequently somewhat different from this mem- 

 ber in most representatives of the order; and that these characters, 

 coupled with an elongated body, enabled it to swim quite well by lateral 

 oscillations with little or no help from the pedes. 



The only alteration in the pes of this animal is that there is a thin, 

 cutaneous extension of the lateral border. This is believed to be for 

 the purpose of enabling the feet to present fewer inequalities when they 

 are folded back against the base of the tail during swimming. As a 

 matter of fact it is doubtful if anyone knows just how the feet are then 

 held and these lateral extensions of the foot may have some entirely dif- 

 ferent function. Dobson (1882) has shown that in this genus there is 

 a very remarkable specialization of the hip musculature. Evidently the 

 femur is fixed by its flexor muscles, and with this bone thus acting as 

 an origin the caudofemoralis or gluteus maximus extends far back- 

 ward onto the tail (fig. 47), thus helping in the lateral oscillations of 

 this member. There has been no definite reduction in the length of 

 the femur as in the desman, and Dobson stated that although in gen- 

 eral form the pelvis resembles that of Centetes it is narrower and with- 

 out a true symphysis, interpubic connection being ligamentous. 



The river otters are of particular interest in the present connection 

 because I regard it as most likely that the terrestrial ancestors of the 

 Cetacea were beasts of very similar body form, namely, with long, 

 sinuous trunk, short legs, and powerful tail, especially at base. The ot- 

 ter is such a playful creature that it is often difficult during observa- 

 tion to be sure which actions are concomitant to greatest efficiency in 

 swimming, and which are attributable to exuberance of spirits. In the 

 common genus Lutra the hind limbs are frequently kicked in a sort of 

 galloping action, seldom entirely rhythmically but at odd intervals. I 



[299] 



