Again, the large intestine is better developed in the higher animals, in mammalia and to a lesser degree in birds, in whom the functional demands for nutrition are active and require that a relatively large amount of food should pass through the digestive tract in a given time. On the other hand in the lower cold-blooded vertebrates the metabolism is less active, less food is taken and it is not necessary to secure all the nutrient material contained in the same for the organism. The great differences observed in the vertebrate series in regard to length, width and structure of the large intestine depend upon these physiological conditions. The divisions of the human large intestine into caecum, ascending, transverse and descending colon, sigmoid flexure and rectum are found only in the primates, and here not uniformly. In the lower vertebrate classes the endgut is very short, corresponding only to the pelvic segment of the Mammalia (rectum), a colon proper being absent in these forms (cf. Fig. 112, _Echelus conger_). The human large intestine exhibits a very characteristic structure. Throughout the greater part of the colon the longitudinal muscular layer is mainly disposed in the form of three bands or taenia (ligamenta coli). The canal itself is longer than these bands, thus producing a folding of the walls in the form of three rows of pouches (cellulae coli), in the intervals between the bands. The pouches of each row are separated from each other externally by constrictions, internally by projecting crescentic folds (plicae coli) (Figs. 471, 472 and 474). This arrangement of the large intestine is also found in the monkeys (Fig. 473) and in certain Rodents (Fig. 474). In other mammals the large intestine is smooth and cylindrical and the longitudinal layer of muscular fibers uniform (Fig. 475). In general the vertebrate large intestine is _wider_ than the small, usually in the proportion of 5:1 or 6:1. In some ruminant Herbivora, however, the great length of the colon leads to a reduction of the caliber in certain segments so that the large intestine does not exceed the width of the small, or even falls below the same. The _length_ of the large intestine, as in man, is usually much less than that of the small intestine. As already stated this disproportion is more marked in Carnivora than in Herbivora. The ratio in length of the large to the small intestine is very low in the Seals (1:14), and in several Edentates, as _Myrmecophaga_, _Tamandua_ and _Bradypus_ (1:9-11). In the carnivorous mammals it ranges 1:5-7. In some of the ruminant Herbivora, as the cow and sheep, it is 1:4, while in the deer, horse, certain Rodents (as _Lepus_ and _Cricetus_) it reaches as high as 1:2 or 1:3. The large intestine is usually relatively short in birds, reptiles, amphibia and fish. In the Cassowary the length of the large to the small intestine is 1:6. In some of the birds of prey (eagle) the proportion falls as low as 1:68 or 70.