282 DISEASES OF CATTLE. 



upon another. In some of the more simple joints the bones fitting 

 one into another are held together by the dense structures around 

 them, admitting of very little or no movement at all, as the bones of 

 the head. In other joints the bones are bound together by dense, car- 

 tilaginous structures, admitting of only limited motion, such as the 

 union of the small bones at the back part of the knee and hock (meta- 

 carpal and metatarsal) . In the more nearly perfect form of joint the 

 power of motion becomes complete and the structures are more com- 

 plex. The substance of the bone on its articular surface is not cov- 

 ered with periosteum, but is sheathed in a dense, thin layer of carti- 

 lage, shaped to fit the other surfaces with which it comes in contact 

 (articular). This layer is thickest toward its center when covering 

 bony eminences, and is elastic, of a pearly whiteness, and resisting, 

 though soft enough to be easily cut. The bones forming an articula- 

 tion are bound together by numerous ligaments attached to bony 

 prominences. The whole joint is sealed in by a band or ribbonlike 

 ligament (capsular ligament) extending around the joint and at- 

 tached at the outer edge of the articular surface, uniting the bones 

 and hermetically sealing the cavities of the articulation. This struc- 

 ture and the articular surface of the bone is covered by a thin, deli- 

 cate membrane, known as the " synovial membrane," which secretes 

 the joint oil (synovia). This fluid is viscid and colorless, or slightly 

 yellow, and although it does not possess a large quantity of fat, its 

 character somewhat resembles oil, and it serves the same purpose in 

 lubricating the joints that oil does to the friction surface of an 

 engine. Although the tissues of the joint when used in a natural 

 way are able to withstand the effect of great exertion, when un- 

 naturally used, as they are very delicate and complex, they are liable 

 to inflammatory and other changes of a very serious nature. The 

 synovial membrane, and in fact the whole structure of the joint, 

 is susceptible to injury and serious inflammatory derangement, and 

 the capsular ligament is liable to be distended from excessive secre- 

 tion of synovia. The latter process may be almost noninflammatory, 

 and attended with little inconvenience or importance other than a 

 blemish to the animal, which in cattle is not serious. It may occur 

 on the back part of the leg above the fetlock or on the inner and fore 

 part of the hock, corresponding in its location to windgalls and bog 

 spavin of the horse. Continuous support by bandages will generally 

 force reabsorption, and as the limb is not subjected to violent action, 

 as in the case of the horse, the affection is not so liable to recur. 



SPAVIN. 



Occasionally working oxen that are used in the lumber woods and 

 made to pull heavily, with bad footing, are afflicted with this con- 

 dition. When it occurs lameness is the first symptom. During the 



