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Pig. 1. — Vermiform Appendix, Caecum, and parts of Small In- testine and Colon of Rabbit (Lepus cuniculus), with the Peyerian and also some of the mesenteric glands in connexion with them injected. The ileum and colon lie side by side, the former describing a siphon-shaped curve before ending in a dilatation, known as the ' sacculus rotundus,' and homologous with the aggregation of Peyerian follicles situated in man just anteriorly to the ileo-caecal valve. The sacculus rotundus occupies the centre of the figure ; above and a little to the left of it another somewhat similar aggregation of Peyerian follicles is seen just beyond the ileocolic valve. The colon curves backwards externally to and concentrically with the ileum. The caecum consists of two portions : one larger in calibre, thinner in walls, and sacculated spirally ; the other, the homo- logue of the human ' appendix vermiformis,' smaller in calibre, but with much thicker walls. It has been injected as described in the text, and the injection is seen to have passed into some mesenteric glands situated close to the junction of the two segments of the caecum, and between it and the colon.