OF THE DIGESTIVE ORGANS. 



I. — Of the Alimentary Canal. 



§ 127. The basis of tlie alimentary canal is formed by the so- 

 called coats. The innermost of them, the mucous membrane, 

 corresponds in structure to the external skin, and, like this, has, 

 1, a non-vascular covering, composed of cells — the epithelium ; 2, 

 a basis composed of connective and elastic tissue, containing vessels, 

 nerves, and different forms of small glands ; often, also, furnished 

 •with special outgrowths (papillce, villi), and traversed by smooth 

 muscular fibres — the nutcous membrane, strictly so called; and 3, 

 a lavcr of loose connective tissue, situated externallv — submucous 

 tissue. The second coat, the muscular coat, contains, for a certain 

 extent, at the commencement and termination of the tube, 

 transversely striped muscular fibres; in other parts, smooth 

 muscular fibres, which elements mostly form two layers, an outer 

 "with longitudinal, and an inner with circular fibres, more rarely 

 three distinct layers. Lastly, the third or serous coat exists only 

 upon the part of the alimentaiy canal which lies in the abdomen 

 and pelvis, and is a delicate, translucent, epitheliated membrane, 

 with few vessels and nerves, which covers the tube and connects 

 it with the walls of the abdominal cavity and with the abdominal 

 viscera. 



II. — Of the Oral Cavity. 



A. OF THE MUCOUS MEMBRANE OF THE OEAL CAVITY. 



§ 128. The commencement of the alimentary canal has, so to 

 speak, only one covering, the mucous membrane, which is more 

 or less firmly attached to the bones and muscles bounding the oral 

 cavity, and is distinguished especially by its not inconsiderable 

 thickness and red colour, which is due to its copious supply of 

 blood-vessels, as also by its numerous nerves and papilla. 



The proper mucous membrane, although continuously connected 

 at the lips with the corium, and gradually passing into the latter, 

 is more transparent and softer than the corium ; it is, nevertheless, 

 very firm and also more extensible. It consists, like the thinnest 

 parts of the corium, of a single layer, cri'" to o'2'" in thickness, 



