ANIMAL LOCOMOTION. 45 



disposed in a number of vertical lines. These creases are espe- 

 cially well seen in the skin of tiie hog. (Series 675. See p. 93.) 



It is a noteworthy fact that the number and the position of 

 the folds on the side of the hog are the same as those of the bands 

 seen on the side of the trunk of the nine-banded armadillo, and 

 it becomes an interesting matter for consideration whether or not 

 the bands may not have originated in the same manner, and for 

 some reason remained permanently. 



The position of backward strain, as already announced, is most 

 variable for the fore limb. The strain is not, however, the same 

 for all animals. The backward inclination of the humerus is 

 greatest in the deer. It is pronounced in the other ungulates, 

 excepting the giraife. In the elephant it is scarcely discernible. 

 (See p. 91.) 



It is evident that the limb that leaves the ground the last is 

 the one which does the most work. This function probably varies 

 at different times in the same gait, although there is nothing in 

 the photographs which proves that such variation occurs. 



The amount of forward strain is also subject to variation. The 

 deer possesses extraordinary power to throw the fore limb for- 

 ward. The degree to which the facility to accomplish this act is 

 carried is seen in series 690, Fig. 10. It is also marked in the 

 raccoon (series 744, 745). The movement is much less marked 

 in the horse and the ungulates generally. The deer exhibits a 

 much larger anterior surface at the trochlear curve of the distal 

 end of the humerus than does any other mammal which was ex- 

 amined. In the deer the proportion is one-sixth of the shaft of 

 the humerus, in the ox and horse about one-eighth. 



The sudden release of the backward strain, with eversion of 

 the foot, must naturally tend to inversion of the knee ; hence a 

 simple torsion of the entire limb is effected. (See Torsion, p. 57.) 



The 3Ianner of a Limb going " of in the " Spring." 



The nature of the "spring" is not made clear by all the photo- 

 graphs. It is well seen in the horse (series 642), but in the dog 

 the immense impetus which is gained by the "spring" would appear 

 to be produced by a mechanism altogether inadequate to the end 

 in view. The animal rises from the ground without the source 

 of the necessary power to accomplish this act being evident. In 



