134 PHYSIOLOGY. 



great distance. To keep up a circulation sufficient for the part, and 

 no more, nature has varied the angle of the origin of arteries accord- 

 ingly. Thus we find that near the heart the arteries arise by obtuse 

 angles ; some of them reflected ; which become more and more so, till 

 they arise by very sharp angles. The more remarkable instances of 

 this are in the intercostal arteries ; because there is not another set of 

 arteries in the body whose origins are so much the same, whose offices 

 are so much the same, whose distances from their origin to the place 

 of use [distribution], and whose uses are so much the same. There- 

 fore, if there be any difference in the angles at the origin of the 

 arteries at equal distances from the heart, it must be with regard to 

 the distances of their insertion [termination?] from the heart. And 

 there is such a difference. Even the arteries that arise from the in- 

 tercostals are much more obtuse at the beginning of the intercostals 

 than at the termination. 



The reason that it is not so evident in all the arteries, is that there are 

 not two arteries on one side of the body that take the same course, go 

 the same distance, and are to do the same thing ; for some parts re- 

 quire a stronger circvdation than others, which will make a difference in 

 the origin of two arteries, supposing they go the same length and the 

 same course. 



We see the same thing in the secondary arteries, such as the sub- 

 clavian. It sends its branches off near its origin by much more obtuse 

 angles than it does further on ; for in this artery all the branches are 

 to do nearly the same things, and are to go nearly the same length, 

 which was what we observed in the intercostal and lumbar arteries. 



The vasa vasorum seem to come from a neighbouring artery, not 

 from the artery that it supplied. This we see in dissecting them. But 

 to see if some of these should arise from the artery itself, I injected a 

 carotid artery out of the body, but none of the vasa vasorum were 

 injected. 



The nearer you come to an artery in the living body, the less the 

 pulsation is either felt or seen ; and when dissected bare, the motion of 

 the blood is not to be seen or felt with the finger in the least 1 [viz. in 

 Dr. Hunter's servant's sister's external carotid]. 



1 [That the arteries are dilated during the pulse, Flourens saw by enclosing the 

 abdominal aorta, in a rabbit and in a dog, hi a ring made of very fine watch-spring, 

 the ends being merely in contact : at every stroke of the heart these ends were di- 

 varicated, but in a very slight degree. Weitbrecht (De Circul. Sang. Cogit. Physiol.) 

 was the first who saw that the principal cause of the pulse was the displacement of 

 the artery by the jerking power of the heart.] 



