20 THE ARMY HORSE IN ACCIDENT AND DISEASE. 



The pelvis is composed of two segments. In each segment are 

 three united, irregularly shaped, flat bones, namely, ilium, ischium, 

 and pubis (haunch bones). The ischium and pubis bones are also 

 united in pairs, forming the floor of the pelvic cavity occupied by 

 the bladder and rectum. The two ilium bones or branches are 

 triangular in shape. The outer angle in each case is the point of 

 the hip. The two inner angles are close to each other, and together 

 form the point of the croup. Just below this point each branch is 

 attached to the sacrum by ligaments. That portion of the ilium 

 extending back to the hip joint is called the "shaft." 



The hind leg is composed of the following bones: Femur, thigh 

 bone ; tihia, leg bone ; fibula, accessory leg bone ; patella, stifle bone ; 

 tarsus, hock (made up of six small bones; named calcaneum, astrag- 

 alus, cuneiform raagnum, medium and parvum, and cuboid) ; large 

 metatarsal, cannon bone; two STnall metatarsals, sphnt bones. Below 

 the cannon, the bones have the same name as in the fore leg. 



JOINTS. 



A joint is a movable union between two or more bones. Covering 

 the adjacent surfaces in the joint is a thin and very smooth layer 

 of a jjeculiar kind of cartilage called articular cartilage. A lubricating 

 fluid, synovia, joint oil, is required to reduce the amount of friction; 

 this fluid is secreted or formed by the synovial membrane and the 

 latter is confined and protected by the capsular ligament which com- 

 pletely surrounds the joint. Outside of the capsular ligament are 

 binding hgaments holding the bones in position. 



The joints of the fore leg are as follows: Shoulder joint, formed by 

 the lower end of the scapula and the head of the humerus; elhow 

 joint, by the radius, ulna, and humerus; knee-joint, by the radius, 

 seven small bones (carpals), and the upper end of the metacarpals; 

 fetlock joint, by the large cannon, upper pastern bone, and the two 

 sesamoids; pastern joint, by the upper and lower pastern bones; 

 coffin joint, by the lower pastern, cofRn bone, and shuttle bone. 



The following joints make up the articulation of the hind leg: 

 Hip joint, formed by the socket of the pelvis and the head of the 

 femur ; stifle joint, by the lower end of the femur, head of the tibia, 

 and the patella ; hock joint, by the lower end of the tibia, six small 

 bones (tarsals), and the upper ends of the metatarsals. The fet- 

 lock, pastern, and cofiin joints correspond to those of the fore limb. 



LIGAMENTS. 



Ligaments are, generally speaking, strong bands of white fibrous 

 inelastic tissue. Their principal use is to firmly bind joints together, 

 thereby preventing vibration and diminishing friction. 



