688 Journal of Agriculture. [8 Nov., 1907. 



varies in diflferent parts. In the mouth, pharynx, oesophagus and crop 

 it is of the character known as stratiBed epithelium and functions as a 

 protective membrane only ; in the true stomach, caecum, colon and rectum 

 the epithelium is columnar and is depressed into simple tubular glands 

 (Fig. 45) ; in the small intestine there are not only these small depressions 

 but between them are elevations or villi which markedly increase the 

 surface. Immediately external to the epithelium is a delicate band of 

 smooth muscle called the muscularis mucos.^ which by its contraction 

 can pucker the epithelial layer. External to this is a layer of loose 

 connective tissue called the submucous coat which allows the epithelial 

 layer some freedom in altering its shape and which generally contains 

 a few mucous glands. The latter secrete a glairy tenacious fluid, 

 mucous, consisting chiefly of water, mucin and salts, which is poured on 

 the surface of the epithelium and which acts as a lubricant as well as 

 a protection to the exposed cells. The next layer is a strong band of 

 smooth muscle disposed circularly, whilst external to this is another strong 

 band of smooth muscle dispyosed longitudinally. In those parts of the 

 tube that lie in the abdominal cavity (crop to beginning of rectum) we 

 have another coat external to this longitudinal muscle called the serous 

 or PERITONEAL COAT which is reallv a sheet of fibrous tissue thrown round 

 the .ube but not completely enclosing it, and continuous with the same 

 sheet lining the inner wall of the abdominal cavity. Thus the tube is slung 

 in the abdominal cavity by a double layer of fibrous tissue, called the 

 MESENTERY, in which run the vessels and nerves supplying the various 

 coats of the tube. The peritoneal or serous coat on its exposed surface 

 is very smooth and is constantly moist, so that the various organs can 

 move about without friction. 



A.w. 



Fig. 44. Diagram to show arrangement of mesentery. A.W., abdominal wall; 

 P., peritoneal coat lining abdominal wall and reflected over gut; M., mesentery. 



The structure of the villi deserves some special mention. These 

 projections, which give a velvety appearance to the mucous membrane of 

 the small intestine, are lined, as has been stated, with columnar epithelium; 

 within this is found a layer of blood vessels; wuthin this a thin band of 

 smooth muscle; whilst most centrally is placed a small vessel ending in 

 a knob which vessel belongs to the lymjihatic system (to be discussed 

 later) and is called a lacteal. 



THE GLANDS OF THE ALIMENTARY CANAL.— The mucous 

 membrane of the mouth, pharynx, oesophagus and crop is kept lubricated 

 by small mucous glands in the sub-mucous layer. In the mouth however 

 are found the openings of the ducts of special masses of glandular tissue 

 called the salivary glands. The secretion of these glands is called 

 saliva or spittle. In the stomach the tubular glands, described above, 

 secrete gastric juice. In the intestines the secretion of the tubular glands 

 is called succus entericns. The tubular glands of the colon secrete a 

 large amount of mucus as well as succus entericus. 



Opening into th^ duodenum, or first part of the small intestine, are 

 the ducts of the two largest glands of the body, the liver and the 



