TEXTURE OF THE ARTERIES. 167 



Hunter, whose observations were generally made with the 

 most scrupulous attention to perfect exactitude, were often re- 

 peated, so as to make one confirm another; and who has, re- 

 ceived that sanction of greatness in which one's posthumous 

 reputation becomes more exalted than the living; bestowed 

 much attention on this subject. He was induced to believe 

 that this middle coat was formed by a muscular lamina inter- 

 nally, and an elastic one externally; which distinction might 

 be rendered evident by cutting a contracted artery through 

 tra?isversely, when the muscular coat would be found projecting 

 beyond the other. He acknowledges, however, that he never 

 could discover the direction of the muscular fibres; though he 

 supposed them to be oblique, because their degree of contrac- 

 tion was greater than a straight muscle could produce. 



The elastic contraction of an artery, is manifested both in the 

 direction of its length and of its circumference; for, when put 

 upon the stretch in either way, it has the ability of returning to 

 its original dimensions after the distending force ceases. The 

 muscular contraction, however, only occurs in the circumference, 

 and not at all in the length : by it the caliber of arteries is re- 

 duced to a very small diameter, if an animal be slowly bled to 

 death. If, in this "contracted condition, an artery be slit open 

 longitudinally, the elastic coat will, at the cut margin, project 

 beyond the other, which Mr. Hunter considers as another way 

 of ascertaining the existence of the two tunics. But if this same 

 artery be then stretched transversely, the muscular coat will 

 project beyond the other; for the reason, that if a muscle, after 

 death, be elongated by force, it has no power of returning from 

 that state, but will remain precisely as it is: whereas, elasticity 

 being a property of matter enjoyed quite as fully in the dead as 

 in the living state, the elastic coat of the artery returns to the 

 medium condition. 



Mr. Hunter, with a view of satisfying himself on these several 

 points, had a horse bled to death, so as to obtain the vessels, at 

 their minimum of contraction. A circular section of the aorta 

 measured, at first, five inches and a half, and, on being stretched, 

 it lengthened to ten inches and a half; being let alone, it con- 

 tracted to six inches, at which it remained stationary; the dif- 

 ference between six inches and ten and a half was then the 



