338 STRUCTURE OF THE SHEEP. 



its substance, and it becomes organized. So, likewise, if a 

 part be wounded, the divided vessels throw out clots of 

 blood, which adhere to the surface of the wound ; the red 

 particles become absorbed, the glutinous fibrine organized, 

 and the breach is thus gradually restored. Thus we see 

 how important it is that the blood should possess its peculiar 

 properties, its state of fluidity, and its disposition to coagu- 

 late : if the former did not exist, the blood would . be ob- 

 structed in the capillary vessels, and the vital functions 

 could not be carried on ; and if' deprived of its coagulating 

 property, no wounds could heal, or loss of substance be re- 

 stored, but the most trifling cut would be the precursor of 

 death. 



The quantity of blood contained in the body is very -dif- 

 ficult to ascertain ; for if an animal be bled to death, a good 

 deal will still remain in the blood-vessels. It has, however, 

 been estimated to be about one-fifth the weight of the body; 

 and of this, about three-fourths are contained in the veins, 

 and one-fourth in the arteries. In young animals there is 

 more than in old ones, as in them the body must not only be 

 sustained, but increased in size. It is likewise more abun- 

 dant in wild animals than in tame ones, and in proportion to 

 the vigor of the animal. 



The Heart is a strong hollow muscle, of a conical shape, 

 with its base towards the spine, and its apex towards the 

 left side, against which it is thrown at every contraction. 

 It is double, having a right and left side, the former contain- 

 ing black, and the latter red blood ; the right side is the 

 thinnest and weakest, being devoted to the lesser office of 

 the circulation of the lungs : the left the stoutest, having to 

 govern the general circulation of the system. Each of 

 these halves consists of two cavities, an auricle and a ven- 

 tricle ; the former, which derives its name from its resem- 

 blance to a dog's ear, is considerably thinner than the latter, 

 and is situated towards the base. The heart is formed prin- 

 cipally of fleshy fibres, connected together by cellular tis- 

 sue, whence it obtains its elasticity ; and its surfaces, both 

 internal and external, are lined by a transparent membrane. 

 The blood is prevented from moving in a retrograde course 

 by means of a number of valves : there are three in the 

 left ventricle, the edges of which are connected by tendi- 

 nous cords (cord(B tendinai) to small fleshy eminences on the 

 inside of the ventricle, called carnea columruB, or fleshj^ 



