STRUCTURE AND ECONOMY OF THE HORSE. 19 



witli a sufficient quantity of saliva, which is chiefly secreted by the 

 parotid glands at the root of the ear, is then conveyed into the 

 stomach by means of a long muscular tube which passes throuo-h 

 the cavity of the chest. In the stomach the food is acted on 

 by a peculiar fluid called the gastric juice, and is then passed 

 into the small intestines, Avhere the chyme, as the food is then 

 called, becomes mixed with the bile, a yellow fluid secreted by 

 the liver. Both the small and large intestines are fastened to 

 the spine by means of a strong membrane called the mesentery, 

 which, besides veins and arteries, is furnished with a vast number 

 of small vessels called lactcals. These lacteals open into the in- 

 testines, and there absorb the nutritious part of the food, which 

 is a white milky fluid called the chyle, and convey it to a vessel 

 running along the course of the spine, which empties itself near 

 the heart into the circulatory system. Thus by these means the 

 blood becomes enriched with nutriment, and is thus enabled to 

 sup])ly the constant waste the system is continually undero*oino-. 



The blood, being furnished with nutriment, requires to be 

 purified before it is fit for circulation : for this purpose it passes 

 into the right side of the heart, by the muscular contraction of 

 which it is sent to the lungs, where it becomes exposed to the 

 action of the atmosphere, by which it is changed from a dark to 

 a light red colour, and, being freed from impurities, it enters the 

 left side of the heart, and from thence is sent, by means of the 

 arteries, to all parts of the body, sujjplying every part with 

 nourishment, and also the various glands of the body not only 

 with their own proper nourishment, but with materiel for the 

 secretion of their peculiar fluids. Thus, the salivary glands 

 separate the saliva from the blood ; the pancreas furnishes a 

 juice somewhat similar; the testicles secrete the semen; and the 

 kidneys the urine. Each gland separates its pecuhar 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 tlie 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 onwards by the influence 

 of their peculiar action, and, having had the nutritious part ex- 

 tracted, are excreted from the body generally in a solid form. 



The cellular membrane is a very elastic substance, and enters 

 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 



