MANUAL FOR STABLE SERGEANTS. 17 



coffin joint, formed by the second and third phalanges and the navicular 

 bone. 



20. The joints of the hind limb, named from above downward, 

 are the sacro-illiac joint, formed by the sacrum and ilium; the hip 

 joint, formed by the hip bone and the femur; the stifle joint, formed 

 by the femur, the patella, and tibia; the tarsal (hock) joint, formed by 

 the tibia, the bones of the hock, and the large and small metatarsal 

 bones. The joints below the hock are named and formed the same 

 as in the fore limb. 



THE MUSCLES. 



21. Muscles are the active organs of motion and are classified as 

 voluntary and involuntary. Voluntary muscles are those under direct 

 control of the will, as the muscles of the leg and tail. Involuntary 

 muscles are those not under direct control of the will, as the heart 

 and the muscles of the intestines. The voluntary muscles form 

 about 45 per cent of the weight of the body. 



22. Muscles are composed of a contractile part, which is red in 

 color and forms the flesh; and a tendinous part, which is usually 

 attached to the bones but may be attached to other muscles. Ten- 

 dons are similar in structure to ligaments, being composed of white 

 inelastic fibers. Their function is to treansmit to the point of attach- 

 ment the power generated by the contraction of the fleshy portion of 

 the muscle. 



23. With regard to their form muscles are classified as long, wide, 

 and short wide muscles surround the body cavities. Short muscles- 

 are found near the joints and irregular shaped bones. Long muscles 

 are found in the limbs, in the neck, and along the back. 



24. A muscle is an extensor when its action is to extend, or 

 straighten, a joint; it is a flexor when its action is to flex, or bend, a 

 joint. The following paragraphs (25 and 26) contain a brief descrip- 

 tion of a few important extensors and flexors of the limbs. 



25. Muscles of the fore limb (fig. 5, 6). 



(a) The common digital extensor (common extensor of the foot) 

 (fig. 5c). This is the principal extensor of the fore leg and foot. It 

 originates at the lower extremity of the humerus, and its fleshy por- 

 tion continues to the lower end of the radius, at which point it 

 becomes tendinous, passes downward over the knee, and continues- 



106233 17 2 



