74 <Wf THE MOTION OF THE BLOOD. 



127. \V« must now enqoire what power* are exerted 

 by other organs m assisting the circulation. The exist- 

 ence of some secondary powers and their ability to as- 

 sist, or even in some cases to compensate for, the 

 action of the heart, are proved by several arguments : 

 ▼. c. the blood moves in some parts to which the in- 

 fluence of the heart cannot reach, — in the vena porta? 

 and placenta; not to mention instances of the absence 

 of the heart.* 



128. The principal of these powers is the function of 

 the arteries, not easy indeed to be clearly understood 

 and demonstrated. 1. They have a muscular coat. (E) 

 2. That they are irritable, has been proved by repeated 

 experiments, f 3. The size of the soft nerves arisimr 

 from the sympathetic, and surrounding the larger arte- 

 rial branches, particularly in the lower part of the 

 abdomen, % argues the importance of these vessels in 

 assisting the motion of the blood. § 



129. The arteries pulsate, and indeed violently, so 



• 



* See v. C. C. W. Curtius. Dt monstro hitmano cum infante gemello. Lugd. 

 fiat. 1762. 4to. p. 39. W. Cooper, Philos. Transact, vol. lxv. p. 316. 

 Haller, Opera Minora. T. iii. p. 33. C. Chr. Klein, Descriptio moustrorum 

 on until dam. Stuttg. 1793. 4tO. 



+ Wahrr Verschuir, lit arttriar. et vttutr. vi irritabili ; rjusqut in vasts 

 tmettnt; et inde oriunda sanguinis directions abnormi. Gronintr. 1766. 4 to. 



Rich. Dennison, Diss, artcrias omncs et vcnarvm partem irritabiUtate prse- 

 ditasetse. Edinb. 1775. 8vo. 



Chr. Kraiup, lit vi vital* arteriarum. Argent 1785. 8vo. 



X Observe for instance, in Walter's Tabula ntrvor. thorac. tt abdominis, the 

 right hepatic, Tab. ii. O. Tab. iii. /. — the splenic, tab. ii. P. Tab. iii. m. tab. 

 ir. o.— the superior mesenteric, Tab. ii. O,. Tab. iii. ». — the inferior mesenteric, 

 Tab. ii. T. — and many others. Compare Socmmerring, Dt c. A. fabrica. 

 T. ir. p.3C2. 



( Haller, lit Ntrvor. in arterias imptrio. Gotting. 1744. 4to. Luccr, I.e. 



