20 ARBOREAL MAN 



primitive third segment as well. We may now say that 

 we have rescued the third segment as a hand, and so 

 preserved it from ever becoming a mere paw or a hoof. 

 This is most important perhaps as important a thing 

 as ever happened in any evolutionary story for the 

 permanent preservation of a primitive hand, affixed to 

 a primitive rotating forearm, made possible a great 

 number of the most far-reaching developments. 



By a primitive hand we mean a very definite thing, 

 and one essential in the make-up of this hand is the 

 possession of five separate, and fairly equally developed, 

 digits. We have made use of the water-newt to picture 

 some stages of fore-limb development, but we may not 

 press comparisons with this type into minute details. 

 The hand of existing Amphibians does not fulfil all the 

 demands of our definition, for only four digits are present 

 in living tailed members, and four well-developed digits, 

 with a rudiment of a fifth, in living tailless forms. But 

 there are several extinct forms of generalized Amphibia 

 and Reptilia which had what we may truly term a primi- 

 tive hand, and among the living and unspecialized 

 Reptilia it is still to be met with. It is a very remark- 

 able fact that in the numerical development of the 

 individual bones which compose the separate fingers, the 

 Chelonians (Tortoises and Turtles) are the match of 

 Man and his nearest mammalian neighbours. There is 

 evidently something extraordinarily primitive about the 

 hand that has been preserved and passed on to Man ; but 

 like the primitive rotating forearm, this primitive, simple 

 and unspecialized five-fingered hand is full of possibilities. 

 These possibilities are given their chance of development, 

 and are made the most of under the circumstances we 

 are picturing circumstances which include the emanci- 

 pation of the fore-limb as one of the effects of the dawn 

 of arboreal life. This primitive hand possesses muscles 

 which can move it upon the ulna and radius at the wrist- 

 joint, and muscles which can bend the fingers in towards 



