[Distribution of the muscle coat at the pars pylorica in swine stomach].

Distribution of the muscle layers around the pars pylorica of the swine stomach was examined. In the antrum pyloricum of the pars pylorica, a distinct stratified structure of the tunica muscularis was found and the muscle bundles of the stratum longitudinale showed rectangular crossing over those of the stratum orbicularis. In the canalis pyloricus of the pars pylorica, on the contrary, stratified structure was indistinct. It is because the running direction of the muscle bundles changes continuously from longitudinal to orbicular layers. In the tunica muscularis of the canalis pyloricus, the authors successfully identified two wide streams of muscle bundles, which were supposed to play an important role in the mechanism of closing the ostium pyloricum. One of the streams was such muscle bundles that distributed annularly around the distal end of the canalis pyloricus forming a broad thick plate inside the curvature ventriculi major. The plate was thick at the curvatura ventriculi major, then became thin toward the curvature ventriculi minor, and finally disappeared. The second of the streams was such muscle bundles that distributed annularly in an area from distal to central part of the canalis pyloricus and, turning its direction to the distal end of the curvatura ventriculi minor, ran in the canalis pyloricus obliquely. Finally it entered into the torus pyloricus where it ran brush-wise, inclining distally, to the tip of the torus pyloricus, and ended as a stump-like form. It is clear that these two streams of muscle bundles functions to narrow the lumen of the distal portion of the canalis pyloricus at the phase of either contraction or relaxation.(ABSTRACT TRUNCATED AT 250 WORDS)