THE ONE BIG DIGIT OF THE HORSE 361 



the ancestral form of the Dolphin's hand (Globicephalus. me/as) as 

 delineated in Flower's Osteology of Mammals, p. 302, in which two 

 of the digits remain almost Plesiosaurian, and the remaining three 

 are vastly modified by atrophy. 



In this Round-headed Dolphin, the carpus has become 

 differentiated from the metacarpus and phalanges with a probably 

 greater mobility of the hand. Here is a comparison of the hands 

 of two Dolphins, showing the number of phalanges, including the 

 metacarpals, as given in Flower's Osteology of Mammals, p; 303 : 



Globicephalus melas. Delphinus. 



thumb, . . . four . . . two 



index, . . . fourteen. . . ten 



middle finger, . . nine . . . seven 



ring finger, . . . three . . three 



little finger, . . one . . . one 



So that in closely allied animals the number of phalanges can 

 be vastly different. 



It is not known whether the Ichthyosaurs and the Plesiosaurs 

 were oviparous or viviparous. Hawkins, in the book of the Great 

 Sea-Dragons,^. 1 8, says 'We had hitherto supposed these Sea- 

 Dragons oviparous, and now we are tempted to think them 

 mammal.' 



Judging from the skeleton of the hand one would be inclined 

 to infer that, like the Dolphin, the Plesiosaur, in spite of its long 

 neck, was a mammal. 1 



When we begin to compare the hands and feet of vertebrates, 

 it is astonishing what modifications they have undergone. For 



1 In reality the distinction between oviparous and viviparous animals is only nominal, 

 for in the Australian Platypus we have an oviparous mammal. 



