(_b_) In other forms, as in the hares (Fig. 465, _IV_, 3), the greater part of the caecum carries a typical spiral fold, continued up to the root of the terminal appendage (Fig. 388), in which segment the mucous membrane is devoid of folds, but studded thickly with lymphoid follicles. Beyond the caecum proper the spiral fold is continued in the opposite direction into the proximal segment of the colon, which is large and capacious and evidently shares both the physiological and morphological characters of the caecum proper, forming so to speak an accessory caecal chamber. Beyond what we thus might term the caecal division of the colon the large intestine becomes reduced in caliber, and the previously continuous spiral fold becomes broken up into separate semilunar haustral plicae, corresponding to the superficial constrictions between the colic cells. In structure this distal segment of the rabbit colon closely resembles the human large intestine (Fig. 474). One of the most marked examples of this secondary modification of the colon is presented by the intestinal canal of another Rodent, _Lagomys pusillus_ (Fig. 391). The caecum of this animal is long, curved, provided with a well-developed spiral fold. The terminal segment of the pouch is reduced to an appendix, with smooth mucosa containing adenoid tissue, as in the rabbit. A second adenoid appendix, representing the globular saccus lymphaticus of the rabbit, is derived from the caecum at the ileo-colic junction. The first segment of the colon beyond the ileo-colic junction is dilated and sacculated, the caecal mucous fold being prolonged into it. This is succeeded by a narrow smooth-walled second segment. The third division of the colon is again dilated and sacculated, followed by a short fourth smooth-walled section. A fifth stretch is again provided with colic cells, beyond which the terminal segment continues of uniform caliber and with smooth walls to the vent. The colon therefore presents three distinct sacculated portions whose structural modifications suggest that they function in the same sense as the caecal pouch proper. In man and in other Primates the crescentic colic plicae are disposed in a more or less evident spiral manner around the axis of the intestine, and it is not difficult to recognize in them the modified remnants of the typical spiral valve of lower forms. On the other hand, in conformity with the general reduction of the caecal apparatus, the mucous membrane of the large intestine in Carnivora is smooth and devoid of any trace of the spiral fold (Fig. 475).