120 



OF THE ARTERIES GENERALLY. 



ings, united to form one elastic tube : the external coat is of 

 condensed cellular tissue ; whose elastic powers are so con- 

 siderable, as to preserve the cylindrical form of the principal 

 canals when empty. The middle coat consists chiefly of yellow 

 elastic tissue; and the internal coat is serous tissue, or 

 similar to synovial membrane. By their elastic power' the 

 arteries are capable of being distended : by this likewise 

 they can adapt themselves to a smaller quantity of fluid 

 than usual. It is by this elasticity, which operates longi- 

 tudinally as well as circularly, that, in cases of injury, the 

 divided ends of an artery retreat within the cellular sub- 

 stance around, and thus close its orifices. When this con- 

 traction is prevented byapartial division only, the hajmorrhage 

 continues ; but even the entire division of the punctured 

 vessel is not generally effective in arteries of the first, second, 

 or third magnitude. The elastic powers appear in dissimilar 

 proportions in difierent horses, as in different men ; from 

 which arises some constitutional phenomena in the indi- 

 viduals of each species ; giving to some a greater disposition to 

 haemorrhage and inflammation, which is called a sanguineous 

 temperament. The elastic coat appears to exist in greater 

 proportion in the horse than in the human being. To this 

 cause it is probably owing, that acute inflammations of the 

 vital organs, in the horse, run through their stages so much 

 quicker, than similar affections in our own race. To this 

 power it is to be attributed, that a horse can bear the divi- 

 sion of a much larger artery without danger than a man. 



Arteries, in their different courses, send out branches, 

 which freely join with other branches sent out by other 

 arteries ; in consequence of this circumstance we are able 

 to deprive the horse of large and essential vessels; the 

 small arteries which have united with others then enlarging, 

 and thus carrying on the circulation. Most arteries termi- 

 nate by means of their capillary branches in veins ; we 

 know this, because we can empty the arteries, by drawing 

 the blood from the venal trunks ; and because injection 

 forced into the arteries, in many instances enters the veins ; 

 but is prevented from so doing if the fluid used be of a 

 coarse description. A more scarce termination of arteries 

 is in cells; from which veins arise to take it up again, as 

 m the spleen, &c. Difl'erent parts ai'e more or less plenti- 



