[Illustration: FIG. 512.--Human foetus at term (negro). Caecum and ileo-colic junction; ventral view. (Columbia University Museum, No. 692.)] [Illustration: FIG. 513.--Human foetus at term. Caecum and ileo-colic junction; dorsal view. (Columbia University, Study Collection.)] [Illustration: FIG. 514.--Human foetus at term. Caecum and ileo-colic junction; dorsal view. (Columbia University Museum, No. 1715.)] Figs. 513 and 514, also taken from the foetus at term, show the caecum from the dorsal aspect and illustrate well the sharp character of the curve which carries the apex of the pouch up and to the left. All the variations observed in the adult caecum are derived from these two foetal types by a subsequent and usually asymmetrical enlargement and dilatation of the pouch. We can consider the derivatives of each form separately. =I. Adult Caeca Derived From Type I.= (schema, Fig. 509, _I^a_, Fig. 510). 1. Further development leads to an enlargement of the caecal pouch and a sharper demarcation between the same and the appendix. The resulting caecum is symmetrical, with equally developed lateral sacculi, between which the termination of the longitudinal muscular bands and the root of the appendix is situated (schema, Fig. 509, _I^b_). [Illustration: FIG. 515.--Human foetus at term. Caecum and ileo-colic junction; ventral view. (Columbia University Museum, No. 1510.)] [Illustration: FIG. 516.--Human foetus at term. Caecum and ileo-colic junction; ventral view. (Columbia University Museum, No. 1548.)] In Figs. 515 and 516 two infantile caeca are shown which illustrate this form. The narrow and pointed apex of the foetal conical caecum is replaced by the capacious pouch which is differentiated sharply from the appendix. Among the anthropoid apes the same type is seen in the caecum of the gibbon (Figs. 455 and 456), and of the young chimpanzee shown in Fig. 460. 2. An increased development of the caecal pouch in the adult leads to the protrusion caudad of two symmetrical sacculations on each side of the root of the appendix which appears between them. The original apex of the caecal pouch is still marked by the implantation of the appendix and by the termination of the longitudinal muscular bands, but the lowest level of the pouch is found on each side of this point at the fundus of the secondary lateral sacculi (schema, Fig. 509, _I^c_). Treves, to whom belongs the credit of first accurately describing and classifying the forms of the adult caecum based on the development, found this type in three of a series of 100 cases examined. [Illustration: FIG. 517.--Adult human caecum and ileo-colic junction. (Columbia University, Study Collection.)] [Illustration: FIG. 518.--Adult human caecum and ileo-colic junction. (Columbia University Museum, No. 234.)]