THE HORSE IN MOTION. 41 



propelling forces alone are called into play, and every muscle " of the 

 line " has to contribute its part, and the action is automatic. 



The muscles not employed as propellers or carrying weight are 

 few and small, as we have seen, bearing no comparison to the others. 

 We will consider the latter in their order, commencing with the great 

 gluteus (Plates III., IV., V., c, c, c,). It is a muscle of the first rank. 

 As seen in the plates, it reaches forward over the loins and adheres to 

 the strong aponeurosis, or tendinous membrane overspreading the ilio 

 spinalis. It passes over the concave border of the ilium, or ridge 

 between the hip and the angle of the croup, covers the upper surface 

 of the ilium and the ligaments that cover its openings, and is at- 

 tached to the spines of the lumbar vertebra and those of the sacrum ; 

 it is also attached to the strong aponeurosis that covers it externally 

 like all superficial muscles of the back. This aponeurosis is repre- 

 sented as dissected away in the plate. Its fibres all converge outward, 

 downward, and backward to their insertion into the great trochanter 

 behind the head of the bone, best represented in Plate V., e, c, c. (The 

 great trochanter is so largely developed that it forms the short arm of 

 a lever, bent at almost a right angle to the shaft of the bone, whose 

 length does not exceed four inches from the head of the bone as a 

 fulcrum.) The length of its longest fibres is twenty-six inches, and 

 its average weight in two well-bred mares * was found to be sixteen 

 pounds. It occupies a very advantageous position to give speed to the 

 movements of the leg. The length and volume of its muscular fibres 

 enable it to keep up a sustained action from the time the hind foot 

 takes the ground under or in advance of the centre of gravity, until 

 it leaves it after completing its propulsive effect. When the foot is 

 off the ground it furnishes the sinews of war, offensive and defensive. 

 The distance from the insertion to the fulcrum or head of the bone 

 being so short, it causes the foot when free from the ground to move 

 with great velocity. 



* The weight of the animal from which the measurements and weights of muscles are given 

 was about 1,100 lbs. These figures must not be considered absolutely correct, but relatively. 

 In a horse regularly worked the muscles will be found to be heavier than in the better bred but 

 idle ones sacrificed on the altar of Science. 



6 



