LOCOMOTOR SYSTEM 



599 



the strain from the flexor metatarsi muscle. That the cord 

 is not absolutely essential to standing may be determined ex- 

 perimentally by dividing it, or clinically by the rupture which 

 occasionally occurs. It is the antagonist of a similar tendo- 

 ligament at the back of the tibia, which runs from the femur 

 to the calcis, the function of which is to oppose hock-flexion 

 (see Fig. 191, 2). 



The dotted lines indicate the 

 powerful mechanism for 

 maintaining the limb in a 

 rigid condition, i, i. The 

 muscles which keep the pa- 

 tella drawn up and the stifle- 

 joint locked ; 3, the flexor 

 of the hock and metatarsus 

 automatically affected by 1 ; 

 2, The gastrocnemius and 

 flexor perforatus muscles, both 

 keeping the hock extended 

 in opposition to 3. In 2 

 and 3 tendinous cords run 

 from end to end, and so act 

 as ligaments, keeping the parts 

 in the relation prescribed by 

 the patella without great 

 muscular effort. 4, The per- 

 foratus below the hock ; 

 5, the perforans ; 6, the check 

 ligament ; 7, the suspensory 

 ligament ; 8, the extensor of 

 the foot ; 9, the gluteus 

 maximus keeping the hip- 

 joint extended. 



Fig. 191. 



-Bones of the Hind-Leg of the Horse in the Attitude of 

 Standing. 



The Hock. — The muscles which keep the hock extended 

 (Figs. 191, 2 ; 192) are — (1) The gastrocnemius, running from the 

 femur to the calcis, to which it is attached. It is an active 

 extensor when the foot is off the ground, a passive extensor when 

 the weight is resting on the limb. (2) The superficial digital flexor 

 (flexor perforatus), which runs from the femur to the calcis, to 

 which it is attached, forming a tendinous cup into which the 

 point of the calcis fits, and subsequently running down the back 

 of the limb to be inserted into the second phalanx. This muscle 



