Even although in working oxen there is no tendency to overfeeding, the animals remain none the less predisposed to diseases of the digestive apparatus; the meal times are often too short, and rumination has to be performed under the yoke or during work—in a word, under unfavourable physiological conditions. =Semiology.= To ensure correct diagnosis it is necessary here, perhaps more than in any other department of pathology, to be capable of grasping the symptoms or syndromes and signs afforded by the different parts of the digestive apparatus; to know how to co-ordinate and group them so as logically to deduce the final synthesis, the diagnosis. The diagnosis proving correct, the prognosis becomes easy, and this is the chief object from the economic standpoint. The practitioner who undertakes treatment knows how to deal with the case, and the owner likewise knows what he undertakes to do. Although this classification may appear arbitrary, we shall consider successively diseases of the mouth, of the pharynx, œsophagus, stomach, intestines, etc., firstly describing the symptoms characterising these diseases. At the same time we should state that many symptoms are common to a large number of diseases and in themselves have absolutely nothing characteristic. They are simply sign-posts capable of showing the way. =Mouth.= External examination reveals the condition of the muzzle, the lips and their commissures, and the surroundings of the buccal opening, and detects the existence of any desquamation, rents, eruptions, ulcerations, etc., which may be present. In quiet animals the practitioner can examine the cavity of the mouth single-handed, but in troublesome animals it becomes necessary to have an assistant, who seizes the muzzle with one hand and the tongue with the other, or who simply fixes the animal’s head. In exceptional cases it will be necessary to secure the patient to a post, tree, or wall. The mere attempt at examination will show whether there is trismus or absolute freedom of movement in the jaws. [Illustration: $1] By introducing the fingers between the commissures and applying them to the bars or to the free portion of the tongue, the practitioner will be able approximately to estimate the local and general temperature. The sensations experienced will also inform him of the degree of moisture or dryness of the mouth and of its sensibility.