AXIMAL LOCOMOTIOX. 37 



when the forearm is held iu semipronation. Such a motion is of 

 importance in describing the wing of the bird and the bat. The 

 term Planation is here thought to be convenient, since it expresses 

 the fact that the movement of the hand is in the plane of the 

 flexor surface of the forearm. Planation includes both pronation 

 and supination. Cont7-apkmatio)i as easily indicates a movement 

 at an angle to the plane of the flexor surface of the forearm. It 

 embraces flexion and extension, and is not especially demanded, 

 except that a term which includes both flexion and extension as 

 well as abduction, as used in the sense of abduction of the thumb, 

 may be acceptable. 



In like manner it has been found useful to employ terms for the 

 different orders of the foot-falls. 



Synchiry indicates that the right and left foot of a single pair 

 act together. Thus in the canter, gallop, and the run, the horse 

 moves all the feet synch i rally. The movement of the lower limbs 

 in man is also synchiral. The feet may act alternately or together. 



In the strictest sense all mammalian limb-motions are synchiral, 

 — i.e., the right and left parts of a single pair move alternately. 

 This motion is at its maximum in the trot, and at its minimum in 

 the spring as performed by the kangaroo. The term is intended 

 to apply to the act in which the feet succeed each other on the 

 ground. The alternation of the right and left hind legs on the 

 ground, while the fore legs are in the air, is a posterior synchiry; 

 and in the same way the alternation of the fore legs on the ground, 

 the hind legs being in the air, is an anterior synchiry. The rabbit 

 appears to resort to synchiry as an alternation of the walk even in 

 the slowest rate of movement ; but, as a rule, it may be said that 

 synchiry is an expression of a fast gait. 



Asynchiry wowld naturally embrace the movements in which 

 the feet act in combinations of hind and fore feet. But since these 

 movements are varied and important, it has been thought desirable 

 to substitute a positive term, and the word heterocMry^ is proposed. 

 The walk, the trot, and the rack are heterochiral, since the fore 

 foot is followed, not by its fellow, but by a hind foot. When the 



*''While assuming the responsibilitj' for this word the writer desires, at tlie 

 same time, to say that it was suggested to him in a conversation with his 

 friend. Professor T. N. Gill. 



