THE TRUNK. 



I may explain that the convexity of a curve may be 

 measured by the proportion which its height {c d Fig. 174 

 or Fig. 175) bears to the length of its cord, a b. Thus, \i c d 



is equal \.o \ a b \n Fig. 174, and equal X.o \ a b in Fig. 175, 

 the curve a c b will be three times as convex in the former, as 

 in the latter. 



Among the higher animals, we find that chest capacity 

 is obtained either by convexity or by length. Hence, those 

 species which have short chests, have round ones ; and those 

 that have long ones, have them flat-sided ; the capacity being 

 increased by roundness of the ribs, and decreased by flatness 

 of these bones. We have already seen that undue length 

 of body is detrimental to speed, weight-carrying power, 

 and strength in draught. Consequently, we should seek for 

 roundness of chest in order to obtain good breathing power. 

 Youatt, in his book on The Horse, appears to have originated 

 a fallacy concerning the conformation of the ribs, which has 

 been repeated by many English writers. He says that " the 

 circular chest could not expand, but every change of form 

 would be a diminution of capacity." This statement seems to 

 be based on the supposition that the chest expands and con- 

 tracts, by the ribs opening and closing in a direction at right 

 angles to the length of the body. Instead of this being the 

 case, the difference in capacity of the chest is due to the fact 

 of the ribs, which are inclined to the rear, turning round 

 towards the front on their upper and lower ends, as on pivots, 



