Arrangement of the tunica muscularis in the ileal papilla of swine.

The arrangement of the bundles of muscular fibers in the ileal papilla was studied in 32 adult male crossbred swine by dissection of the muscular bundles in this region, after immersion in 50% nitric acid, and by observation under the stereomicroscope of material preserved in a 10% formaldehyde solution. In the ileal papilla, the cranial (ileocolic) contour of the tunica muscularis was formed by the circular strata of the ascending colon and the ileum, and the caudal (ileocecal) contour by the circular strata of the cecum and the ileum. The longitudinal stratum was located between the circular strata with predominance of muscular bundles originating in the terminal ileum. The tunica muscularis showed an increased thickness at the base of the eminence and at the free border, not reaching the apex. In the ileal papilla, the circular and longitudinal components characterize a "pylorus", the ileocecocolic or ileal pylorus as a transit regulation device for the flow of contents between the small and large intestine of swine.