26 Traces of Unity in the 



action of elastic ligament, which again is only the 

 ordinary ligament of the part, shortened and made 

 resilient : in the edentata, at the extremity of the ungui- 

 culate sub-class, as in the echidna, the claws, still five in 

 number, with sometimes the rudiment of a sixth, as in 

 the spur of the male ornithorhynchus, or in the scraper 

 of the mole, are enormously developed, encasing the 

 ends of the fingers on all sides with the exception of a 

 button-hole-like slit on the underside, and being much 

 more like hoofs than claws : and in this way a point \B 

 reached from which it is not difficult to pass on, through 

 various transitional forms, of which the most remark- 

 able instance is met with in the hind foot of the extinct 

 Megatherium, to the more ordinary forms of hoof. In 

 this hind foot, indeed, (not so in the fore foot, where 

 there are three huge claws) there is a combination of 

 unguiculate and ungulate characteristics which is not to 

 be met with elsewhere, for of the three large toes which 

 are present (two, the ist and the 2nd, are absent) one, 

 the 3rd, supports an enormous pick-like claw, while the 

 other two, the 4th and 5th, terminate in tuberous pha- 

 langes which were evidently encased in hoofs. 



There is a wide gap between the foot or hand of man 

 and the parts corresponding to it in the horse, but it is 

 one which is easily bridged over. The hand of the 

 Ateles, or spider-monkey, differs from that of man or the 

 orang in being thumbless, or all but thumbless ; the 

 thumb of the orang is much smaller than that of man : 

 in each case the part which disappears or tends to dis- 

 appear is the thumb. And so also in vertebrate crea- 

 tures of still lower grade. The fore-paw of the bear or 

 cat has the full number of five fingers ; that of the dog 

 has four fingers with a very rudimentary thumb sup- 

 porting the dew-claw, and appearing at a considerable 



