THE MOTION OF THE BLOOD. 183 



in the vena portae and placenta; not to mention instances of 

 the absence of the heart. P 



" The principal of these powers is the function of the arteries, 

 not easy indeed to be clearly understood and demonstrated. 1. It 

 is well known, that they have a peculiar coat, which is all but 

 muscular. 2. That they are irritable, has been proved by re- 

 peated experiments. <i 3. The size of the soft nerves arising 

 from the sympathetic, and surrounding the larger arterial branches 

 with remarkable networks, particularly in the lower part of the 

 abdomen r , argues the importance of these vessels in assisting 

 the motion of the blood. 5 



" All know that the arteries pulsate, and indeed violently, 

 so that if, v. c. we place one leg over the other knee, we. find not 

 only that it, but even a much greater weight, may be raised by 

 the pulsation of the popliteal. Hence an alternate systole and 

 diastole, corresponding with those of the heart, have long been 

 assigned to them. 



" But this, although commonly believed on the evidence of 

 sense, is open to much question 1 : it may be asked, especially, 

 whether this pulsation is referable to the power of the artery, or 

 only to the impulse given by the heart to the blood propelled into 

 the aorta. 



P " See v. c. C. W. Curtius, De monstro humano c.um infante gemello. Lugd. 

 Bat. 1762. 4to. p. 39. 



W. Cooper, Phil. Transact, vol. Ixv. p. 316. 



And, instar omnium, Fr. Tiedemann, Anatomic der Kopflosen Missgeburten. 

 Landshut, 1813. fol. p. 70. sq." 



i " Walter Vershuir, De arteriar. el venar. vi irritabili: ejusque in vasis excessu; 

 et inde oriunda sanguinis directione abnormi. Groning. 1766. 4to. 



Rich. Dennison, Diss. arterias omnes et venarum partem irritabttitate preeditas 

 esse. Edinb. 1775. 8vo. 



Chr. Kramp, De vi vitali arteriarum. Argent. 1785. 8vo." 



r " Observe, for instance, in Walter's Tabuke nervor. thorac. et abdominis, the 

 right hepatic, tab. ii. O. tab. iii. /. the splenic, tab. ii. P., tab. iii. m., tab; iv. o; 

 the superior mesenteric, tab. ii. Q., tab. iii. /.the inferior mesenteric, tab. ii. T* 

 - and many others. 



Consult Soemmerring, Dec. h.fabrica. t. iv. p. 362." 



s " Haller, De Nervor. in arterias imperio. Getting. 1744. 4to. 



Lucai, 1. c." 



* " T. Kirkland, Inquiry into the present state of Medical Surgery. London, 

 1783. 8vo. vol. i. p. 306. sq. 



But especially Cal. Hillier Parry's Experimental Inquiry into the Arterial 

 Pulse. Lond. 1816. 8vo." 



