graphs of a fore leg on the ground at the gallop (plate by 

 Marey and Pages). 



There are five positions of the leg numbered o, i, 2, 

 3,4. 



At position o the foot strikes the ground, at 4 is has 

 just left the ground. 



It is seen that during the whole time of rotation, the 

 scapulo-humeral angle is closing and has the following 

 values : 



Values of the S capulo-Humeral Angle. 

 Position o 133° 



I 130° 



" 2 120° 



3 118° 



At position 4, when the foot leaves the ground, the 

 angle quickly opens to 130°. 



But the closing of the scapulo-humeral angle is accom- 

 plished in a very pecular way : during the whole rotation 

 the scapulum continues to rise from the horizontal and 

 its inclination is as follows : 



correspond to the precise movement when the arm rises sharply 

 toward verticality to cause the lifting of the fore hand. 



At this moment reasoning would show that all of the leg below 

 the arm should be a rigid column, and consequently should be without 

 angles ; if not, the effort of the arm would tend to close the angles 

 and a part of the energy expended by the arm would be lost. For the 

 same reason the contraction of the muscles which support the shoulder 

 must be such that the scapulum shall be motionless in spite of the 

 force exerted by the arm. 



It seems clear that the motion of the humerus is controlled by 

 the sterno-humeral muscles, and the longer the lever arm by which 

 these muscles act the easier the movement. The runner with a rela- 

 tively long humerus should therefore have a long period of suspen- 

 sion. The length of the arm appears to be diminishing in our 

 present day Thoroughbred. According to M. de Gaste, the propor- 

 tional length of shoulder to arm is 1.94 to 1 with the present Thor- 

 oughbred ; according to the measurements of the horse Fitz-Gladiator, 

 it is 1.55 to 1; in the trotter it is 2.04 to 1. (de Gaste.) 



The rotation of the phalangian lever begins and ends at the same 

 time as that of the leg, but it presents the peculiarity that it has in 

 the beginning a movement in the opposite direction ; this lever passes 

 from P to P', and again passes through P to P". The distance P P' 

 depends upon the elasticity of the pastern and that is a function of its 

 length. We must, therefore, shorten the pastern if we hasten the 

 rotation of the leg in order that the rotation of the phalanges shall 

 end with that of the leg. The pastern of the present day Thorough- 

 bred is shortening, hence the frequency and seriousness of bone 

 troubles. 



I8 



