THE ARTERIES AND THE ARTERIAL CIRCULATION. 283 



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when the vessel takes a curved or serpentine course, its elongation 

 and the increase of its curvatures may be observed at every pulsa- 

 tion. This may be seen, for example, in the temporal, or even 

 in the radial arteries, in emaciated persons. It is also very well 

 seen in the mesenteric arteries, when the abdomen is opened in the 

 living animal. At every contraction of the heart the curves of 

 the artery on each side become more strongly pronounced. (Fig. 

 92.) The vessel even rises up partially out of its 

 bed, particularly where it runs over a bony sur- 

 face, as in the case of the radial artery. In old 

 persons the curves of the vessels become perma- 

 nently enlarged from frequent distension ; and all 

 the arteries tend to assume, with the advance of 

 age, a more serpentine and even spiral course. 



But the arterial pulse has certain other pecu- 

 liarities which deserve a special notice. In the 

 first place, if we place one finger upon the chest 

 at the situation of the apex of the heart, and an- 

 other upon the carotid artery at the middle of 

 the neck, we can distinguish little or no difference 

 in time between the two impulses. The disten- 

 sion of the carotid seems to take place at the 

 same instant with the contraction of the heart. 

 But if the second finger be placed upon the temporal artery, instead 

 of the carotid, there is a perceptible interval between the two beats. 

 The impulse of the temporal artery is felt a little later than that of 

 the heart. In the same way the pulse of the radial artery at the 

 wrist seems a little later than that of the carotid, and that of the 

 posterior tibial at the ankle joint a little later than that of the radial. 

 So that, the greater the distance from the heart at which the artery 

 is examined, the later is the pulsation perceived by the finger laid 

 upon the vessel. 



But it has been conclusively shown, particularly by the investi- 

 gations of M. Marey, 1 that this difference in time of the arterial 

 pulsations, in different parts of the body, is rather relative than 

 absolute. By the contraction of the heart, the impulse is commu- 

 nicated at the same instant to all parts of the arterial system ; but 

 the apparent difference between them, in this respect, depends upon 

 the fact, that, although all the arteries begin to be distended at the 



Elongation and curva- 



Dr. Brown-Sequard's Journal de Phvsiologie, April, 1859. 



