CHAPTER II 

 THE NATURAL HISTORY OF MAN 



HARRY BURR FERRIS 



E. K. HUNT PROFESSOR OF ANATOMY, YALE UNIVERSITY 



The fundamental structural unit in man and other organ- 

 isms is a microscopic mass, called a cell, which varies consider- 

 ably in shape and size, and possesses a central spherical body, 

 termed the nucleus. Animals composed of a single cell are 

 called protozoa, those made of many cells, metazoa. Man is 

 a metazoan and it has been estimated that his body is com- 

 posed of more than twenty-six trillion cells. Animals without 

 a longitudinal, dorsal body axis are called invertebrates while 

 those with such an axis are known as vertebrates. Man has 

 such an axis and also possesses other characters common to 

 the vertebrates, such as a bony cavity, dorsal to the body axis, 

 for the hollow central nervous system, and also an internal, 

 segmented skeleton as shown in the serial repetition of ribs 

 and vertebrae. Man is also a mammal in that he possesses 

 mammary glands and hair and has the thoracic cavity, contain- 

 ing the heart and lungs, separated from the abdominal cavity 

 by a complete diaphragm. Because of structural similarities 

 he belongs to the order of primates together with the lemurs, 

 monkeys, and apes. 



Structurally man differs from his nearest relatives, the an- 

 thropoid apes, by differences of degree rather than of kind 

 such as the better adaptation of his feet and vertebral column 

 to the upright position, the non-opposability of the great toe, 



