CHAPTER IV. 



SPLANCHNOLOGY. 



THIS section of the subject treats of the viscera, or organs which 

 occupy chiefly the cavities of the body, and compose respectively 

 the digestive, respiratory, urinary, and genital systems, all of 

 which communicate with the outside world by apertures on the 

 surface of the body. We will describe these systems in the order 

 here given, first noting that in all of them there is a certain 

 similarity in structure, in so far that each consists of a tube or 

 canal, lined by mucous membrane, and provided with various 

 glands and other accessory organs. 



Before treating of these systems, it will be advisable to allude 

 briefly to certain tissues and structures which are closely associ- 

 ated with them. These are epithelium, mucous and serous 

 membranes, and glands. Involuntary muscular tissue which 

 occurs extensively in these organs has been alluded to already. 

 (See p. 157.) 



EPITHELIUM. 



This is a tissue consisting chiefly of cells, which, in one form 

 or other, covers all the free surfaces of the 

 body i.e., the skin and mucous mem- 

 branes ; one variety of it also covers the 

 inner surfaces of closed and air-tight mem- 

 branous sacs, the serous and synovial mem- 

 branes, in which case it is distinctively 

 known as endothelium. The following 

 varieties of epithelium are described : 

 squamous, columnar, spheroidal, and ciliated. 

 Squamous, tesselated, pavemental, or 

 scaly epithelium consists of flattened scaly 

 usually arranged in superimposed layers. In shape 

 270 



Detached epithelium cells 

 from the mucous membrane 

 of the mouth, a, Cell wall; 

 1), Nucleus ; r, Nucleolus. 



cells, 



