166 



COMPARATIVE ZOOLOGY. 



and also the tail, for locomotion and prehension, keeping 

 a horizontal attitude; wiiile the Apes, half erect, as if 

 they were half-quadruped, half-biped, go shambling along, 

 touching the ground with the knuckles of one hand and 

 tlien of the other. In descending the scale, from the 

 most anthropoid Ape to the true Quadruped, we find the 

 centre of gravity placed inci'easingly higher up — that is, 

 farther forward. Birds and Men are the only trne bipeds ; 

 the former standing on their toes, the latter on the soles 

 of the feet. Teri-estrial Birds walk and run ; while Birds 

 of flight usually hop. Tlio Ostrich can for a time outrun 

 the Arabian Horse ; and the speed of the Cassowary ex 

 ceeds that of the swiftest Greyhound. 



V 



<\ 



CHAPTEE XVIIII^ 



THE NEEVOU8 SYSTEM. 



Nervous Matter exists in the form of cells and 

 fibres. Ill the cellular state it is grayish, and accunui- 

 J,, lated in masses, 



\.mt<!^. . called ganglia, or 



centres, wliicli 

 alone originate 

 nervous force; 

 the fibres are gen- 

 erally white, and 

 arranged in bun- 

 dles, called nerves, 

 ■which serve only as 

 conductors. Most 

 nerves contain two 



Fio. 133. — Nerve-cells from Hiimiin Brain: A, assod- kiuds of fibres like 

 ated with nerve-tnbes and blood-veasels ; B, raulti- , ' 



lioliir nucleated cells. Highly magnified. IH Structure, but 



' See Appendix. 



