Tongue.—A tongue is present in all reptiles. In crocodiles and Chelonia, it is a short, broad, fleshy structure attached to the floor of the mouth over a large area. In crocodiles, a fold on the hinder margin of the tongue engages with a similar structure of the palate, so as completely to separate the air passage from that for food. In lizards the tongue may be flat, broad and not protrusible; it may be narrow, cylindrical and capable of being extended out of the mouth, or its cylindrical anterior half may telescope into the posterior portion, so that the whole can be projected far in front of the snout. This last type reaches its climax in the chameleon (q.v.).
Gut.—In Chelonia, Sphenodon, lizards and snakes, the oesopha gus passes gradually into the stomach, which is, in them, usually spindle-shaped, with its openings widely removed from one an other. In crocodiles, the stomach is placed more transversely, the opening of the oesophagus and the pylorus being approximated. This stomach is an oval sac whose proximal portion is very mus cular, recalling, in its arrangement, the gizzard of a bird; indeed, it customarily contains pebbles used for triturating food. The pyloric end of the stomach is distinct. The stomach always con tains gastric glands.
A pyloric valve usually exists, and the duodenum is not usually sharply marked off from the rest of the small intestine ; only in crocodiles does it form a loop round the pancreas as it does in birds and mammals. The walls of the mid gut are usually thrown into folds or ridges, but seem to contain few or no glands. There is usually or always an ilio-colic valve separating the mid from the hind gut; immediately beyond this the latter gives rise to a caecum in some lizards and snakes. The rectum ends in a cloaca which is usually of elaborate structure.
Copulatory organs are absent in Sphenodon, in Squamata they are a pair of papillae capable of being protruded through the lateral ends of the transverse cloacal slit, and of being retracted, being turned inside out by the contraction of special muscles derived from the tail musculature. Each has a groove on its lateral surface which extends on the wall of the cloaca nearly to the opening of the vas deferens. In crocodiles and Chelonia, a median unpaired penis arises from the ventral wall of the proc todeum; it can be erected through the activities of corpora cavernosa, and is then extruded through the anterior end of the longitudinal cloacal slit. The dorsal or posterior surface of the penis is furrowed by a deep groove, which is probably converted into a canal during erection. The groove leads backward to the openings of the seminal ducts.
The proctodeum is separated by a ridge which is, in effect, a sphincter, from the urodaeum, into which the ureters, vasa defer entia, oviducts and bladder open. A bladder is found in Spheno don, Chelonia and most lizards; it is absent in all other reptiles. The urodaeum is partially subdivided in many reptiles; in snakes a dorsal recess receives the ureters and gonoducts; in crocodiles they open into the dorsal side of the urodaeum, whilst in Chelonia they discharge directly into the neck of the bladder. In Spheno don, lizards and snakes, the oviducts open rather dorsally, in crocodiles and Chelonia ventrally, the vasa deferentia having a similar opening in all forms.
The urodaeum is, in some aquatic Chelonia, produced into a pair of their walled sacs on the dorsal side, which are constantly filled and emptied of water, thus serving as accessory respiratory organs. In all reptiles except crocodiles and Chelonia there is an additional cloacal chamber, the coprodeum, which serves for the storage of faeces.