5. Describe the symptoms of infectious ophthalmia of ruminants and the treatment. CHAPTER XIII GENERAL DISEASES OF THE LOCOMOTORY APPARATUS GENERAL DISCUSSION.--The movements of the different parts of the animal body depend on the union of the bones that form the skeleton (Fig. 28), and mode of insertion of the muscles. The bones meet and form _joints_ or _articulations_. These are divided into three classes: _movable_, _mixed_ and _immovable_. Nearly all of the articulations in the extremities belong to the movable class. The articulations between the bodies of the vertebrae belong to the mixed, and those between the flat bones of the head to the immovable class. [Illustration: FIG. 28.--Skeleton of horse.] The bony surfaces that meet and form the different types of articulations are held together by ligaments (Fig. 29). Sometimes the ligament is placed between the bony surfaces, but usually it is attached to the margins of the articular surfaces that it unites. The _immovable class_ possesses fibrous-like ligaments that are placed between the margins of the flat bones that form the articulation. The _mixed articulations_ are united by a fibro-cartilaginous pad that is firmly attached to the articular faces of the bones, and by peripheral ligaments that may be flat or formed by scattered fibres. All _movable articulations_ are formed by bony surfaces encrusted with a thin cartilaginous layer that makes them perfectly smooth, ligaments and complimentary cartilages. Sometimes the bony surfaces do not fit each other, and we find between them _fibro-cartilages_ that complete the articulation by adapting the articular surfaces to each other. _Round_ or _flat ligaments_ may extend from one articular surface to the other, and attached to the margins of the articulation are _membranous, flat_ or _round ligaments_. Muscles and tendons that cross the articulations should be included among the structures binding them together. [Illustration: FIG. 29.--Photograph of model of stifle joint, showing: ligaments; complementary cartilages; femur; and tibia.] Movable joints possess a _synovial membrane_. This membrane lines the structures that enclose the articulation and secretes a fluid, _the synovia_, that lubricates the surfaces. _The muscles_ are the contractile organs that move the body. The movement of the different parts of the body is rendered possible through the manner in which the skeletal muscles are inserted into the long bones, by which the lever motion is possible. A muscle originating on one bone and terminating on another either moves both bones toward each other or, if one attachment is fixed, the movable is drawn toward the fixed part.