III. CARPUS OR KNEE JOINT.--This joint has been explained very thoroughly in the previous chapter. There are three separate articular surfaces in this joint. This joint has a large capsular ligament, and has binding ligaments one above the other, the seventh being at the back of the three in the upper row, and the eight, when present, in a similar position with respect to the lower row. Thus there are three separate articular surfaces in this joint. The upper surface of the carpus articulates with the radius; this forms the hinge joint of the knee and is where flexion and extension takes place. Another articulation between the upper and lower carpus bones give slight motion to the knee, but not so much as the upper articular surface. Between the lower surface of the lower row of carpus bones and the upper extremity of the metacarpal, or cannon bones, is another articular surface which gives motion to the knee. This joint has a large capsular ligament, and has binding ligaments inside and outside. In addition to the flexion and extension movement the knee joint possesses, it also serves as a cushion and relieves concussion of the fore limb. IV. FETLOCK JOINT.--This joint is formed above by the lower portion of the metacarpal, or cannon bone, and below by the part of the os suffraginis or the large pastern bone. At the back of this joint there are two small bones called the sesamoid bones. This joint has a capsular and two lateral binding ligaments. The motion of this joint is a backward and forward or flexion and extension, same as that of the knee. V. PASTERN JOINT.--This joint is situated just above the hoof, and is formed by the lower end of the os suffraginis or large pastern bone and the upper end of the os coronae or small pastern bone. It has a capsular and lateral binding ligaments, same as the fetlock joint. It also has the same motion as the fetlock joint, and is often the seat of what is termed a high ringbone. VI. COFFIN JOINT.--This joint is situated within the hoof. It is formed above by the lower end of the os coronae or small pastern bone, and below by the upper surface of the os pedis or coffin bone. Immediately behind this joint, and articulating with the two mentioned bones, is the navicular, or shuttle bone--it gets its name from its likeness to the shuttle of a sewing machine. This bone when diseased is the seat of navicular disease, or coffin-joint lameness. The action of this joint is very slight forward and backward. JOINTS OF THE HIND LEG.