It must be constantly borne in mind that the shadows described in this research are cast by the gastric contents, not by the stomach itself. Therefore the movements of the organ are not seen directly, but are indicated by their effect on the contained food. Variations in the length and breadth of the stomach can be inferred from changes in the outline of the shadow, but variations in the front-to-back diameter of the organ must be judged from changes in the intensity of the shadow. The form of the active stomach soon after food has been taken is shown in outline in Figure 1. Since the several parts of the stomach are to be mentioned frequently, it will be well to recall them here in their relations to the outline. The larger, cardiac part of the organ lies to the left of a line through _w x_. Into it the œsophagus opens through the cardiac sphincter, or cardia, at _c_. The pyloric part, which includes all of the stomach situated at the right of a line _w x_, is closed by the pylorus at _p_. This part has two divisions: the antrum at the right of the line _y z_, and the preantral part of the pyloric portion, or middle region of the stomach, between the lines _w x_ and _y z_. The lesser curvature corresponds approximately to the anterior border of the shadow _c w p_; the greater curvature to the more extensive sweep, _c p_, along the posterior border. [Illustration: FIGURE 1.] The wall of the cat’s stomach consists of three coats, but as this paper deals only with the functions of the muscular coat, that alone will be described. The gastric muscular fibres are disposed in three sets: an outer longitudinal layer, a middle circular layer, and a set of inner oblique fibres. The longitudinal fibres continue those of the œsophagus, and, radiating over the cardiac end, become more marked along the curvatures than on the front and back surfaces. Over the antrum they lie in a thick, uniform layer. The circular fibres form a complete investment, and are arranged in rings at right angles to the curved axis of the stomach. Towards the pyloric end they become denser and stronger, and at the pylorus form a thick bundle, the pyloric sphincter. Separating the antrum from the rest of the stomach, at _y z_, is a special thickening of the circular fibres, called by the early writers the “transverse band,” and described by Hofmeister and Schütz as the “sphincter antri pylorici.” The oblique fibres start from the left of the cardiac orifice and pass as two strong bands along the anterior part of the dorsal and ventral surfaces, giving off fine fasciculi to the circular musculature; towards the antrum they gradually disappear.