108 OF LOCOMOTION. 



of the feet and sustained by the other, without his ever ceasing 

 completely to rest on the ground. This last circumstance dis- 

 tinguishes walking from leaping and running, movements in 

 which the body quits the earth for a moment and launches into 

 fie air. 



90. In walking, one of the feet is carried forward, while the 

 other is extended on the leg, and as this last member is supported 

 on the ground, its elongation displaces the pelvis and throws the 

 whole body forward. When the foot which was advanced alights 

 upon the ground, the pelvis turns on the femur of that side, and 

 the leg which was at rest behind, is flexed and carried front of the 

 other, touches the earth and in its turn serves to sustain the body, 

 while the other limb by being extended gives a new impulse to 

 the pelvis. By the aid of these alternate movements of flexion 

 and extension each limb in turn bears the weight of the body, as 

 it would do when standing on one foot, and at each step the 

 centre of gravity of the whole mass of the body is pushed for- 

 ward. 



Security in walking is always in a direct ratio to the degree of 

 separation of the feet, and in an inverse ratio to the mobility of 

 the surface that supports us. It is only at the end of a certain 

 time that sailors walk securely upon the deck. When they have 

 once " got their sea legs" it is very easy to recognise them on 

 shore from the habit which they have of considerably separating 

 the feet in walking. 



91. Leaping or jumping is a movement by which a man pro- 

 jects himself into the air and again falls to the ground as soon as 

 the effect of the impulsion is lost. 



92. The mechanism of the leap consists entirely in the previous 

 flexion of the joints and their sudden extension. When a jumper 

 wishes to spring, he shortens himself by folding himself up as it 

 were upon himself; the leg is flexed forward on the foot, the 

 thigh is also flexed back on the leg, and the trunk with the 

 pelvis are flexed forward on the thigh ; and, when one wishes to 

 spring with all his strength, the trunk is flexed upon itself like a 

 spring. In these preliminaries of the leap, the lower extremities 

 and the body describe a series of zigzags. At the moment ol 

 the leap all the articulations are extended at the same instant and 

 .raise the body with such rapidity that it leaps into the air like an 

 elastic rod that had been bent to the ground, and then suddenly 

 abandoned to its elasticity or spring. 



90- What is the mechanism of walking ? 



91. What is leaping/ 



92. What is the mechanism of a leap ? 



