THE HOCK OR TARSAL region is formed by six bones. They are described as forming two rows. In the upper row there are two bones and in the lower four. They form a series of articulations, the same as the bones of the knee. Practically all of the movement occurs in the articulation between one of the large bones in the upper row and the lower extremity of the tibia. It may be mentioned here that this is the most perfect hinge-joint in the body. A very large tendon is attached to the summit of the hock. Other tendons cross and become attached to the hock bones. The regions of the _hind cannon_ and digit are practically the same as the corresponding regions of the forefoot. QUESTIONS 1. Name the different bones of the fore-limb; hind limb. 2. Describe the regions of the shoulder, arm and forearm. 3. Describe the region of the forefoot. 4. Describe the regions of the haunch, thigh and leg. 5. Describe the region of the hindfoot. CHAPTER XV UNSOUNDNESSES AND BLEMISHES GENERAL DISCUSSION.--The value of a horse depends largely on the condition of the limbs and their ability to do the work for which they are intended. This fact is frequently overlooked by experienced horsemen, who give attention to general conformation and action rather than to soundness of limb. Diseases affecting the limbs may be classed as _unsoundnesses_ and _blemishes_. This classification is based on the degree to which the disease interferes or may interfere with the work that the animal is called on to perform. Unsoundnesses interfere with the use of the part or the use of the animal for a certain work; blemishes do not. Such a basis for the classification of diseases does not enable us to place certain diseased conditions of the limbs in the unsound, or the blemish class at all times. A curb may, if it produces lameness, be classed as an unsoundness. If it does not cause the animal to go lame, and the enlargement on the posterior border of the hock is small, it is classed as a blemish. A high splint may place the animal in the unsound class, but usually a low splint is not considered a serious blemish. This classification is based to a certain extent on the relative economic importance of the disease, or the influence that the disease may have on the value of the animal, as well as any interference with the animal's ability to work. RECOGNITION OF THE DISEASE.--The seat of the disease may be in a muscle, tendon, bone or ligament. The general symptom manifested is lameness or pain. The local symptoms are heat, pain, swelling and bony enlargements. The degree of lameness and the character of the local lesions vary greatly in the different cases. When the animal shows a slight lameness and there is little evidence of any local symptom, it requires the services of a skilled and experienced person to locate the diseased part. When the part shows local lesions of disease and the lameness is characteristic, diagnosis is not difficult.