6 



GORILLAS AND CHIMPANZEES 



lumbar. In it man has five, while the ape has but 

 four. But counting the whole number of bones in 

 the spinal column, and regarding each segment of 

 the sacrum as a distinct bone, which to all intents 

 it is, the sum of the bones in each column is exactly 

 the same. 



Although this appears to be a fixed and constant 

 character, it cannot be esteemed as a matter of great 

 importance, since the same thing has been known to 

 occur in the human skeleton, and the reverse has 

 been known in some specimens of the apes, but has 

 never been observed in the chimpanzee. In this 

 respect he appears to be more constant than man so 

 far as we know at present. 



As the greatest strains of the spinal column are 

 laid upon that part in which the sacrum is located, 

 there is a tendency for these segments to unite in 

 order to meet the demand, and since there is the 

 least flexure in that part, the cartilages that lie 

 between them ossify and become rigid. The erect 

 posture of man allows more room in the loins for the 

 fifth vertebra to move, and thus it is prevented from 

 uniting with the segment below it, which is held 

 firmly in place by the two large bones mentioned, 

 while the crouching habit of the ape presses that 

 vertebra firmly against the other, confining it be- 

 tween the two large bones and thus reducing its 

 movement, wherefore the same result follows as with 

 the other sections below. 



Another bone that may be said to differ in 

 structure is that known as the sternum or breast- 



