THE SPECTRE TARSIER 3 



a Structural modification found also in the oralaofoes 

 and mouse lemurs, but noivhere else amongst the 

 inammalia. In other groups of leaping animals the 

 same end — lengthening of the limb — is attained by- 

 other means. Thus the jerboa rat of Algeria has 

 the metatarsal bones (those immediately below the 

 ankle) fused together into a single rod, as in birds. 

 The first and fifth digits have actually disappeared, 

 while the lower ends of the metatarsals (fusion not 

 being quite complete) are provided with facets which 

 articulate with the bones of the second, third, and 

 fourth toes. The Cape leaping "hare" has both 

 foot and toe bones elongated, but not those of the 

 ankle. In the kano-aroos both the lower lee and 

 the foot (but again not the ankle) are lengthened. 

 Curiously enough, the common frog of our English 

 meadows has the ankle elongated in tarsier fashion^: 

 an amphibian, cold-blooded and aquatic, thus shares 

 this character with a warm-blooded arboreal 

 mammal. Doubtless the elongated bones not only- 

 increase the tarsier's length of leap, but also by their 

 elasticity modify the shock of alighting. In our- 

 selves, at any rate, even the small bones and 

 ligaments of the foot by their number and resilience 

 effectually act as buffers : this may be readily 

 demonstrated by allowing oneself to alight first on 

 the heels (shock transmitted direct to calcaneum)and 



1 111 the frog's ankle, however, it is tlie cah-aneniii and the astrarjalas 

 (not the navicular bone) which incxeases in length. 



