131 



In this gait it is to be noticed that two diagonal 

 feet being on the ground and the other two being 

 lifted, the fixed fore-foot of one side leaves the 

 ground just in time for the collateral raised hind- 

 foot to be put down in its place — that on the op- 

 posite side the two feet (a raised fore and a fixed 

 hind-foot) separate widely, the one forward, the 

 other backward — and that, as we think may be 

 recognized by the eye of an observer, the pro- 

 pelling hind foot leaves the gi'ound an instant before 

 its diagonal (the fixed fore-foot) does so. This 

 result seems analogous with the view we have 

 taken of the order of discharge of the two C C 

 forming each S in the snake's locomotion. 



§ 129. Let it be remembered that tiie air in the 

 lungs expands to support every expansion, and 

 condenses to allow every contraction of the chest ; 

 also that these air actions are of two kinds, 07ie 

 central in the lobes proper, coming from the 

 ophidian movement proper, the other terminal in 

 the lung tips, coming from a working added to that 

 of the central S, in order to accommodate the 

 action of the two additional S S, i. e., of idie loins 

 and of the neck, which work with the hind legs and 

 the fore legs (or arms) respectively and to serve as 

 a working pivot for the union of the ophidian and 



