Since reptiles were the first to inhabit dry land, there were several evolutionary changes in the anatomy of reptiles, with one aspect of these changes being the digestive system.
Many of these adaptations can be seen in the mouth of snakes. Since snakes are terrestrial, many changes occur in the salivary glands in the transition from an amphibian to a reptile. These changes in salivary glands and venom glands aid in the immobilizing and swallowing of their prey. The salivary glands found in snakes include the palatine, lingual, sublingual and labial gland. These glands help moisten the prey for swallowing. In venomous and poisonous snakes, such as the Water Moccasin, poison glands are modifications of the labial glands, lying on either side of the head and neck and lead to ducts in the modified front teeth. The teeth of snakes also underwent changes. Venomous snakes have grooved or tubular teeth for the injection or shooting of venom, while vipers have large retractable, tubular teeth.
Directly inside the mouth of snakes is the buccal cavity. This leads to the oesophagus of the snake. In snakes, the oesophagus is very long and may be as long as half the length of the body. The oesophagus of snakes has more internal folds than other reptiles, which allows for the swallowing of large, whole prey. Peristaltic movement by the walls of the oesophagus moves the food downward towards the stomach.
The stomach is a j-shaped organ in which most of the digestion occurs in snakes. The cells of the stomach secrete digestive enzymes and gastric juices that breakdown proteins. The food then passes through the pyloric valve and into the small intestines.
The small intestines are a long narrow coiled tube where absorbance of nutrients takes place. The small intestines is divided into three regions: the duodenum, the ileum, and jejunum.(Same as a human) The liver, which primarily functions in excreting nitrogenous wastes, storing nutrients, and producing bile, excretes digestive enzymes into the duodenum of the small intestines. Also, the pancreas, which produces insulin and glycogen as well, produces digestive enzymes such as lipases, proteases and carbohydrases and secretes them into the duodenum.(Also the same as in a human)
The food moves from the small intestines to the large intestines, through the caecum. The large intestines are the least muscular and most thin-walled structure of the snake digestive system. It passes into the cloacae chamber. This chamber is divided into a copradaeum for receiving faeces and an urodaeum for urine and products of the genital organs, it also absorbs excess water from the faeces, before it is passed out. The rate of their digestion is most dependent on body temperature because they are cold-blooded animals, if their body is heated up, then their digestion will be faster than a snake which is not heated up.