BIOLOGY OF MAN 1157 



cranial cavity and a shunting forward of the eyes. Another arboreal 

 acquisition was a greatly increased power of turning the head from 

 side to side, locating sounds and scrutinising sights. Touch was 

 largely separated off from nose and snout, and concentrated in the 

 hand, which came to corroborate the other sense-organs increasingly. 

 It was also able to feel over most of the body. There was a deep 

 change in the balance of the body on the legs, in the backbone, and 

 in the chest. Very important was a decrease in the olfactory region 

 of the brain, and an increase in the region where sensory tidings 

 from hand and eye and ear stream in — a region, moreover, towards 

 which the originative seats of the motor impulses tend to become 

 approximated. In short, the arboreal apprenticeship with a free 

 hand favoured the evolution of the "neopallium" of the brain. 



The Visualising Trend. — Certainly one of the most epoch- 

 making of evolutionary trends was that which led among mammals. 

 to the increased survival value of vision ; for one of the most striking 

 of anatomical diagrams ever published is that which Prof. Elliot 

 Smith gives of four brains, which illustrate the evolution of the 

 visual area in our own. The first is that of a terrestrial Jumping 

 Shrew (Macroscelides), where the visual area of the cerebrum is 

 small, and the olfactory area large. The second is the brain of a 

 Tree Shrew (Tupaia), a vivacious arboreal Insectivore with very 

 agile movements. "The olfactory area is reduced; and the whole 

 neopallium undergoes an even more pronounced change corre- 

 sponding to a relatively enormous enhancement of the importance 

 of vision, hearing, touch, and skilled movement for an animal living 

 in the branches of trees." {The Evolution of Man, 1924, p. 142.) It 

 may be explained that the neopallium is a receptive, recording, 

 unifying area of the cerebral cortex which becomes large in the 

 higher mammals. It includes various territories which receive 

 stimuli from all the sense-organs, and is also the seat of associative 

 memory; and it would even seem of unifying consciousness. The 

 areas it includes are visual, tactile, motor, acoustic, and prefrontal 

 — the last being concerned with precise adjustments of the eyes 

 (focussing for stereoscopic vision), and with skilled manipulative 

 movements. Whereas the Jumping Shrew's behaviour is dominated 

 by smell, that of the Tree Shrew (in the same family!) is dominated 

 by vision; and the advance is to be correlated, in part at least, with 

 the arboreal mode of life. 



The third brain is that of the Spectral Tarsier (Tarsius), which is 

 generall}^ regarded as an old-fashioned type among the primitive 

 monkeyish animals (Prosimicc), below the level of genuine monkeys, 

 and more nearly related to the "Half-Monkeys" or Lemuroidea. 

 "The visual territory has become very extensive and the olfactory 

 territory still further reduced in size; and this corresponds in 

 behaviour to the definite usurpation, by vision, of the dominant 



