THE HUMAN SPECIES 



Man .... 

 Horses and bears 

 Oxen 



Lions . . 

 Wild boar . 

 Pigs and dogs . 

 Sheep and goats 

 Cats .... 

 Foxes 

 Hares 



Squirrels and mice 

 Among birds much greater ages are attained : 



104-1 10 years 



50 



40 



35 



25 



20 



15 



15 M 



M 



10 



6 



Falcon 



Vulture and raven 



FIG. 100. How a quadruped stands. 



162 years 

 . 110-118 



Birds are, as a rule, longer 

 lived than mammals (especi- 

 ally parrots, geese and owls), 

 and we must not forget the 

 turtle in the Zoological Gar- 

 dens of London, which recently 

 reached the mature age of 1 50 

 years, as well as the huge 

 Sychellion and Aldabra forms, 

 some of which must exceed 

 300 years. 



The view of Metchnikoff 



that life might be infinitely protracted but for the bacteria in 

 the intestines can scarcely be regarded as explaining all cases 

 of senile decay, for the chief cause of muscular weakness, of 

 arterio-sclerosis, of failing mental powers must still remain in 

 man and beast the daily wear and tear of life which slowly 

 exhausts the tissues. 



I. The Skeleton and Muscles. 



Physiologically, these two systems cannot be separated, and 

 they must be dealt with in the same chapter. For without the 

 muscles the bones are a lifeless framework, and the muscles 

 (save, of course, the heart, the diaphragm and unstriped muscle 

 of the entrails) cannot be considered without reference to the 

 bones which they set in motion. 



