PRELUDE TO 
When an animal is carrying itself forward by any system 
of regular motion, its limbs, in their relation to the body, 
have alternately a progressive and a retrogressive action ; 
their various portions are accelerated in comparative speed 
as they extend downwards to the feet, which are subjected 
to successive changes from a total cessation of movement 
to a varyingly increased velocity in comparison with that 
of the body. 
Photographic analysis has demonstrated that quad¬ 
rupeds employ, on the surface of the ground, eight different 
regular systems of progressive motion. They are— 
1. The walk. 
2. The amble, 
3. The trot. 
4. The rack. 
5. The canter. 
6. The transverse-gallop. 
7. The rotatory-gallop. 
8. The ricochet. 
In this enumeration crawling is omitted, it being 
simply a modified system of walking, and subject to the 
same rules. 
Leaping or jumping by the use of all four of an 
15 
ANALYSES. 
animal’s legs can be regarded only as an accidental inter¬ 
ruption to regular progress. 
All other methods which may be occasionally employed 
by, or which it is possible for an animal to use in terrestrial 
locomotion, may be considered as abnormal movements. 
The differences between the step and the stride of an 
animal are not always clearly understood. 
A “ step ” is an act of progressive motion, in which one 
of the supporting members of the body is lifted from the 
ground, thrust in the direction of the movement, placed 
again on the ground, and caused to reassume, either wholly 
or in part, its proper functions of supporting and propelling 
the body. 
A “stride” is a combination of actions in progressive 
motion, which requires each one of the supporting members 
of the body, in the exercise of its individual functions, to 
be—either alone or in association with another supporting 
member—lifted from the ground in its regular sequence, 
thrust in the direction of the movement, placed again on 
the ground, and caused to reassume the same relative 
