LOCOMOTOR SYSTEM 



605 



extensors of the carpus and foot act, straighten the limb at the 

 knee, and put the foot in position to receive the weight of the 

 body when it comes to the ground. The effort to advance 

 the leg is trifling, and the foot having made contact, the limb 

 being in the position shown (Fig. 193), the real work now 

 begins, for the body has to pass over the limb, while the leg 

 remains fixed and rigid from elbow to foot. The muscles 

 which pull it over are the latissimus dor si acting on the humerus, 

 and the large deep pectoral muscle (see Fig. 188), which, running 

 forward from the ninth or tenth ribs 

 and sternum beneath the fore-leg, to 

 the shoulder -joint, pulls the whole 

 shoulder -joint backwards, and causes 

 the body to rotate over the limb. It 

 is powerfully assisted in this by the 

 cervical serratus and trapezius drawing 

 the scapula forwards and upwards, and 

 the large head of the triceps pulling 

 on the ulna. At the end of the move- 

 ment the column of bones is in the 

 position shown in Fig. 194, and the final 

 act of the limb is about to occur — viz., 

 its propulsive motion. To effect propul- 

 sion, the limb remains rigid while the 

 long flexors of the arm straighten the 

 pastern, until little more than the toe 

 of the foot is on the ground ; then, with 

 a sudden sharp contraction of these 

 muscles, the body is propelled upwards 

 and forwards, the limb being flexed 

 (Fig. 195), carried to the front, unbent, 

 and again placed on the ground. 



The Elbow- Joint has already occupied 

 attention, more particularly in con- 

 nection with its locking during the 

 attitude of standing. During locomotion 

 extensive hinge-like motion occurs, which 



is abnormally exaggerated in high-steppers. The hinge has 

 two condyles and a ridge on the humerus, which fit into 

 a reverse moulding on the radius. The internal condyle is 

 much the larger, and occupies about half the entire articular 

 surface. These condyles, during flexion of the joint, turn the 

 knees outwards. If they throw them out too far, the leg below 

 the knee is thrown in, and so causes " brushing " and " speedy 

 cutting. " This movement is best seen from above when mounted ; 

 Though a hinge-joint, the arm appears to describe a semicircle 



Fig. 195. — The Column of 

 Bones forming the Fore • 

 Leg broken up, the 

 Limb shortened by 

 Flexion at Shoulder, 

 Elbow, Knee, Fetlock, 

 and being carried for- 

 WARDS. 



