OF THE MUSCLES, 115 



Gastrocnemius internus. Origin. From the sulcus, 

 above the outer condyle of the femur. Insertion. Into the 

 OS calcis ; and becoming the perforatus tendon, after it has 

 passed the point of the hock, resembles that of the fore leg ; 

 being inserted into the sides of the os corona. 



Action. The external is the principal motor agent ; the 

 internal possesses scarcely more power than is necessary to 

 adapt its tendon to the motion of the limb ; but this want is 

 supplied by the connexion between the tendons. They are 

 the chief retractors of the lower part of the leg ; and upon 

 their power the propulsive energy of the horse mainly de- 

 pends. Much of the beauty of the animal depends also 

 upon their endurance ; as the horse that has the gastrocnemii 

 tendons cut through instantly falls to the ground. A bursa 

 will be found between the two tendons ; and another between 

 the external tendon and the skin. 



Flexor pedis perforans [Plate III. 12). Posterior 

 origin. From the hind and outer part of the head of the 

 tibia ; from underneath the fibula ; also from the posterior 

 border of the same bone ; and from the strong ligament 

 extending from it. 



Insertion. Its tendon resembles the perforans of the fore 

 leg ; excepting that it extends obliquely across the back 

 of the tibia, passing from the outer to the inner side ; its 

 tendon passing over the calcis, through the theca, at the 

 back of the hock. Immediately below the hock it is joined 

 by its accessory tendon ; and lower down receives the liga- 

 mentous band, which originates from the lower bones of the 

 joint, and the head of the great metatarsal bone. From 

 this point it resembles the same tendon in the fore leg; 

 being inserted into the os pedis, under the navicular bone. 



Action. To co-operate with the gastrocnemii tendons, in 

 retracting the metatarsal bones; but also to flex the pastern. 



Flexor pedis accessorius (Plate III. 15. Fig 8. 2). 

 Origin. From the outer and posterior part of the tibia ; and 

 from the fascial sheath of the perforans. It soon becomes 

 tendinous ; its tendon passing through the synovial sheath 

 at the back of the hock, to gain its insertion into the tendon 

 of the perforans. 



Action. To assist the flexor pedis perforans. 



PoPLiTEUs {Plate III. 18. Fig8 .1). Origin. From the 



i2 



