EMANCIPATION OF THE FORE-LIMBS 15 



enable it to walk and run with the very greatest perfec- 

 tion. As a general statement, we have said that the 

 evolution that produces limbs of this type also demands 

 that all four members shall function alike, fore-limbs and 

 hind-limbs being both supporting and ambulatory organs. 

 This statement needs some qualification, since there are 

 certain exceptions to the rule that all four limbs are 

 functionally of equal importance in the Mammals that 

 have taken to a pronograde terrestrial life ; and it is these 

 exceptions that are of interest. In different types of 

 quadrupedal Mammals there may be well-marked differ- 

 ences in the actual method of movement of the limbs in 

 ordinary leisured progression. 



A right fore-limb and a left hind-limb may be raised 

 simultaneously from the ground and swung forwards; 

 this is the mode of the greater number of quadrupeds. 

 Again, a right fore-limb and a right hind-limb may be 

 raised and advanced simultaneously ; this is the ordinary 

 mode of progression of the giraffe. Or, again, the sequence 

 of bringing the limbs into play may vary with the pace 

 at which the animal travels; and then the animal changes 

 its gait and its stride as the pace varies. An altogether 

 different method may manifest itself with this change of 

 gait in response to the demands of pace, and both fore- 

 limbs and both hind-limbs may be raised and advanced 

 alternately. This mode is habitual in the ordinary quiet 

 gait of some animals ; it is the usual way in which a rabbit 

 moves about when feeding undisturbed. In this method 

 of movement the fore-limbs and the hind-limbs may play 

 an equal part, or the hind-limbs may take an increasing 

 share in the work, both of supporting the body, and of 

 urging it forward. In this way a more and more perfect 

 hop is developed; when this method of progression has 

 reached its most advanced stage the fore-limb is freed 

 very thoroughly from its duties of support. Hopping is 

 a specialized development of the pronograde gait; and 

 it has led to some very interesting developments which 



