296 PEELIMINART EEMARKS. 



The tube in question commences at tlie mouth, a capacious 

 cavity, containing the tongue, the teeth, and the palate. The 

 mouth narrows into the pharynx, and the pharynx into a long, 

 narrow tube, called the oesophagus, the lower end of which 

 suddenly expands into a large space or bag, called the stomach, 

 — which in turn also narrows, and terminates in the intestines, 

 which are divided into the large and small. 



The inner surface of this 95 feet of continuous tubing 

 consists of a fine velvet-like membrane, called the mucous 

 membrane, within whose substance are various structures called 

 glands, the duty of which is to secrete certain fluids necessary 

 to the process of digestion. In addition to the very great 

 number of small apertures opening into the digestive tube in a 

 lateral direction, there are two which I may specially name — 

 one from the liver, called the biliary duct, and the other from 

 the pancreas, called the pancreatic duct. 



External to the mucous membrane, but immediately conti- 

 guous, is a thin tube of muscle, the fibres of which traverse the 

 bowel in a two-fold manner — viz., one set running in a direction 

 from the mouth to the tail ; and the other in a circular direction, 

 or around the tube of the gut in a spiral fashion. It is by the 

 action of this muscular tube, aided by the nervous system, that 

 the contents of the intestinal canal are forced onwards. 



Above this muscular tube, and external to and surrounding 

 it in every part, is the peritoneum, that beautiful pale-blue, 

 glistening membrane, which is at once made visible upon freely 

 exposing the contents of the abdominal cavity. 



The intestinal tube and its appendages (the liver and pan- 

 creas) constitute in the aggravate what is called the Digestive 

 Organs ; they are the structures wherein many substances by a 

 process of trituration and the action of solvents upon them are 

 prepared for assimilation to the body of the animal. 



