The Muscles and Their Work. 25 



muscle is proportional to the degree of stimulation given 

 by its nerves, therefore, the more energetic in action, the 

 stronger, other things being equal. 



When speaking of muscles, the fixed end is the origin, 

 the part (or end) it moves, the insertion. Some of the 

 more important muscles are here taken up and their 

 actions, origins and insertions mentioned, those of the 

 limbs being of especial interest, as dealing with locomo- 

 tion. The first muscle seen after the removal of the skin 

 is the one that twitches the skin, the fly- shaker, pan- 

 niculus carnosus, its boundaries are of no particular 

 interest, its actions are, assisting as it is said to, in the 

 expulsion of air from the lungs when highly developed, 

 seen in the race horse. 



When the foreleg is advanced, the shoulder joint is 

 extended and elbow joint flexed, when drawn back the 

 opposite takes place, due to the action of a powerful 

 muscle (triceps extensor brachii) attached at one end to 

 the front of the shoulder blade and point of the elbow, 

 just below the level of the elbow joint. Another powerful 

 muscle (flexor brachii) attached to the point of the 

 shoulder blade and at the other to the head of the bone 

 of the forearm, flexes (bends) the shoulder joint and 

 straightens (extends) the elbow joint. There are other 

 minor muscles that assist in these movements. Three 

 muscles (flexor metacarpi externus, medius and internus) 

 bend the knee, they originate on the back of the arm just 

 above the elbow joint and are inserted to the bone at the 

 back of the knee (trapezium) and the splint bones. The two 

 muscles (extensor pedis and extensor suifraginis), which 

 straighten the fetlock, pastern and coffin joints, run down 



