X. Order: Insectivora.
In the true Insectivora the cæcum is also absent and the alimentary canal a simple non-differentiated tube.
In certain herbivorous animals included in this group on the other hand, such as Galeopithecus (Fig. 419), the cæcum is present as an enormous sacculated pouch with spiral convolutions.
Fig. 419.—Galeopithecus volans, colugo. Ileo-colic junction, cæcum, and colon. (Columbia University Museum, No. 1844.)
XI. Order: Primates.
The cæcum is uniformly present. In certain of the Lemuroidea the terminal portion of the pouch is reduced, forming a species of appendix. A typical vermiform appendix is regularly found in man and in the anthropoid apes, orang, gibbon, chimpanzee and gorilla.
1. Suborder Lemuroidea.
In the typical lemurs the cæcum is long, frequently terminating in a pointed appendage. The proximal segment of the colon is looped and coiled, resembling the spiral colon of the Ungulates and Rodents. Fig. 420 shows the cæcum of Nycticebus tardigradus, the slow lemur, with the typical appendage, and [Fig. 421] shows the spiral arrangement of the proximal colon immediately beyond the ileo-colic junction in the same animal. [Fig. 422], taken from another specimen of the same animal shows the cæcum, appendix and spiral colon. [Figs. 423], [424], [425] illustrate the structure of the parts in three other members of the group, Lemur macaco, Lemur mongoz and Otolicnus crassicaudatus, all showing terminal reduction of the cæcal pouch and tendency to spiral coiling of the proximal colon. In Tarsius spectrum ([Fig. 426]) the cæcum is relatively well-developed, but forms a simple pouch of uniform diameter, without terminal reduction.
