VI. Order: Ungulata.
The intestinal canal, in conformity with the herbivorous habit of the group, is uniformly provided with a large cæcum, and in many forms the proximal segment of the colon immediately beyond the ileo-colic junction is more or less extensively coiled in a spiral manner. This arrangement is, without doubt, to be regarded as being functionally accessory to the cæcal apparatus, in the sense of increasing very much the area of the secreting and absorbing surface and of prolonging the period during which food-substances, which are slow and difficult of elaboration, are retained in this segment of the alimentary canal.
1. Suborder: Artiodactyla.
A. Non-Ruminantia.—In the Suidæ the cæcum is large and the spiral colon well developed (Fig. 368).
Fig. 368.—Sus scrofa fœt, fœtal pig. Ileo-cæcum and spiral colon in situ. (Columbia University Museum, No. 1111.)
In the peccaries (Dicotyles) the terminal portion of the cæcal pouch is reduced, constituting a centrally implanted appendage.
Fig. 369.—Dicotyles torquatus, collared peccary. Ileo-colic junction, cæcum, and spiral colon. (Columbia University Museum, No. 60/1462)
Fig. 369 shows the ileo-colic junction and spiral colon in Dicotyles torquatus, the collared peccary, and Fig. 370 the cæcum and appendix of the same animal detached from the spiral colon. In the hippopotamus, on the other hand, the cæcum is said to be absent. If this is the case the animal forms an isolated exception among the Ungulates.