46 THE HORSE IN MOTION. 



on which it acts as an adductor when the animal is at his ease, but the 

 joint action of these two muscles is as supporters. They have no 

 attachments forward of the centre of motion at the head of the femur, 

 but like the semi-tendinosus they permit the limb to be advanced to 

 the extended position to support the centre of gravity, and then, in 

 common with all the great muscles of the posterior extremity, they 

 support the whole weight of the body, and then only for a limited time 

 do they act as extensors. This will be better understood when we 

 analyze the movements in the gallop. 



There is only one other muscle of the thigh which we will notice, 

 \\-\e gracilis (Plate VI., m). (It is dissected away in Plate VII.) It is 

 superficial on the face of the thigh, and is nearly as broad as it is long. 

 It has its origin on the symphasis of the pubis where it meets its 

 fellow of the opposite side. It is about an inch in thickness in the 

 centre, thins off each way, and is attached to the fascia of the leg 

 for a distance corresponding to its origin at the pubis. It corre- 

 sponds to the gracilis in man, and is called by Chauveau the s/iorl 

 addiuto7'. Its weight is about two and a half pounds. The course 

 of its fibres is downward and about five degrees outward. In its 

 contraction the force is as an adductor about ten per cent, but as a 

 supporter to the weight of the body when it rests on one foot its value 

 is not to be overlooked. 



The want of knowledge of the action of the limbs in locomotion 

 has led the student of anatomy into a too circumscribed view of the 

 action of the muscles. It has led him to give first consideration to 

 forces of secondary importance. It will be seen by a general view of 

 all the muscles of the haunch that those acting upon the thigh bone, 

 or femur, from above are inserted on the outer face of the bone, while 

 those from the lower surfaces of the pelvic bones are inserted into the 

 inner face of the femur. The primary object in both is locomotion, but, 

 from the indirect manner of the application of the forces, they are all 

 necessarily compound ; for example, the great gluteus acts as a pro- 

 peller and fl(5ductor, while the great adductor acts as a propeller and 

 rt'oyuctor, the ^rtyuction of one being compensation for the rt'^duction 

 of the other. In a humanly constructed machine, as a locomotive, 



