STRUCTURE OF THE SHEEP. 295 



Each gland separates its peculiar fluid and no other. The 

 urine being secreted by the kidneys, is conveyed by means 

 of two small but long tubes into the bladder, whence it is 

 excreted from the body. 



The liver is nourished by the arteries, but separates the 

 bile from the dark impure blood, which is conveyed to it by 

 a large vein. The contents of the bowels are passed on- 

 wards by the influence of their peculiar action, and having 

 had the nutritious part extracted are excreted from the body, 

 generally in a solid form. 



The cellular membrane is a very elastic substance, and en- 

 ters largely into the composition of the body : it connects 

 the various glands together, forms frequently a covering for 

 the muscles as well as for various vessels, and exists in the 

 form of cells, which have communication with each other. 



The adipose membrane is found in various parts of the 

 body, and, indeed, secretes the fat, which is deposited in a 

 liquid form, and in small circumscribed bags. The fat thus 

 contained often performs the important office of affording a 

 cushion for parts that would otherwise be exposed to injury ; 

 thus we find that the socket of the eye is abundantly fur- 

 nished with this material. 



There are two other important membranes which are ex- 

 tensively found in animal bodies : they are the serous and 

 the mucous membranes. Whenever an internal part has an. 

 external opening, we find that it is furnished with a mucous 

 membrane which secretes mucus for its protection ; but 

 when the cavity has no external opening, then it is lined 

 with a serous membrane which secretes a thin watery fluid 

 to lubricate the parts, and preserve them from injury by fric- 

 tion. Thus from the entrance of the mouth and nostrils to 

 the anus, throughout the whole internal surface of the bow- 

 els, a mucous membrane exists, by which the fluid is se- 

 creted, the nature of which gives a name to the membrane, 

 and which protects it from injury either by the external air, 

 or by the contents of the bowels. In like manner we find 

 the bladder and urinary organs similarly lined. 



On the other hand, the cavity of the chest and the abdo- 

 men, with their contents, as well as the internal surface of 

 blood-vessels, are furnished with a serous membrane, which 

 secretes a watery vapor. These different membranes are 

 very frequently the seat of disease, and are subject to severe 

 and dangerous inflammation. The admirable manner la 



