Size of Brain (Brain-weight in Grams) 



Various primates 



Gorilla 600 



Chimpanzee 365-400 



Gibbon 95-130 



Earlier forms of man 



Pithecanthropus 900 



Piltdown man 1300 



Neanderthal 1400 



Cro-Magnon 1550 



Modern man 1400-2000 



Various groups of peoples 950-1500 



"One hundred eminent scholars", average weight 1478 



In Brief 



In all the higher animals specialized organs and tissues carry on in an 

 exaggerated degree some special function that is common to all protoplasm. 



Specialized structures are co-ordinated by the activities of sensitive cells 

 called neurons, elaborated in vertebrates into the central brain-spine system, 

 which connects with all parts of the body. 



In all the members of a species the same reflexes occur in practically the 

 same way. A refiex arc is the nerve path consisting of afferent and efferent 

 neurons, with associative neurons. 



Neurons of the central nervous system, that is, those related to knowing, 

 feeling, and voluntary control, are classified according to their functions into 

 (1) afferent nerves, which conduct impulses inward or toward the central 

 portions; (2) efferent nerves, which bear impulses only outward, usually to 

 muscles or to glands; (3) associated neurons, which act as intermediary, or 

 bridging, paths. 



Nerve-endings throughout the body, as well as on the surface, act as 

 receptors for stimuli. Even a simple stimulus frequently sets going a whole 

 group of reactions. 



Many of the so-called "instincts" observed in animals are either reflexes 

 or chains of reflexes. Most of the chains of responses which organisms make 

 appear to be well suited to the situation from which they receive the 

 stimulus. 



Through specialized sense organs animals are sensitive to several varie- 

 ties of stimuli. Species vary in the range of sensitiveness to different stimuli. 



Movements in our bodies are brought about by the action of muscles: 

 striated muscles are subject to voluntary control, smooth muscles are not. 



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