804 Comparative Morphology of Chordates 



notable increase in the complexity of the convolutions of the cerebral 

 cortex. In terms of gross anatomy, these are not "conspicuous" differ- 

 ences. But the greater size implies a larger number of neurons and an 

 increase in the complexity of their relations. In terms of function, these 

 differences may be highly significant in relation to the animal's be- 

 havior, because it is the nervous mechanism of the cerebral cortex 

 which is somehow peculiarly concerned with the animal's capacity for 

 effecting reactions which imply something approaching or attaining 

 intelligence 



The opposable thumb has been referred to as a minor structural 

 characteristic, and so, in itself, it is. To the arboreal primate, however, 

 it is one of great importance. But \\ hen an ape, standing on the ground, 

 grasps a stick and uses it to poke, hit, or move an object, something 

 unique in mammalian behavior appears. The animal is obviously 

 aware that he is not in a tree and he makes no attempt to swing from 

 the stick as if it were an attached branch of a tree. He uses it in a 

 definitely purposeful way as a tool. It requires no strain on the im- 

 agination to think of primitive man using his opposable thumb, in- 

 herited from arboreal ancestors, in grasping sticks, clubs, and stones 

 which served him as weapons and tools. Later he fashioned crude im- 

 plements of stone, then of metal. In the course of many thousands of 

 years, his weapons and tools became more and more elaborate. By 

 use of simple tools he made more complex tools and machines. He 

 devised machines to make tools and to make parts of other machines. 

 Early he learned how to produce and use fire. He availed himself of the 

 energy of moving water and of wind and of the energy released by 

 combustion. Lightning led him to the utilization of electric energy, and 

 most recently he has found a way of releasing incredible and appalling 

 energies by disruption of atomic structure. He has devised machines 

 to serve his every need and he has created for himself a great many 

 new necessities. The present has come to be a "Machine Age." 



Man was primitively a terrestrial animal, but he never acquired 

 more than moderate facility in locomotion on land. He is a poor runner 

 as compared to many quadruped mammals. But he has found ways of 

 compensating for his locomotor mediocrity. He attained the speed of a 

 horse by the simple expedient of sitting astride the horse's back. Then 

 he devised wheeled vehicles drawn by horses. Later, replacing horse- 

 power by engines developing the power of many horses, he rides in 

 self-driven wheeled vehicles which far outspeed the cheetah. Man has 

 no aquatic adaptations. Compared to a seal or dolphin, he is a slow 

 and clumsy swimmer. But he puts himself into a somewhat fish-shaped 

 boat and his pectoral limbs, extended by oars grasped by his prehensile 

 hands, serve as locomotor fins. Or, always seeking ways of avoiding 



