ON THE MOTION OF THE BLOOD. 



65 



with both orders of its own vessels by the openings of 

 Thebesius. * 



100. From this anterior, or, in reference to the heart 

 of some animals, right, ventricle, the blood is impelled 

 through the pulmonary artery into the lungs:, re turning 

 from which, it enters the four pulmonary veins and pro- 

 ceeds into their common sinus and the left, or, as it is 

 now more properly termed, posterior auricle. + 



101. It flows next into the corresponding ventricle ; 

 and then passing into the aorta, is distributed through 

 the general arterial system and the coronary vessels of 

 the heart. J 



102. Having proceeded from the extreme twigs of 

 the general arterial system into the radicles of the 

 veins, and from the coronary arteries into the coronary 

 veins, it finally is poured into the two venae cavae, and 

 then again pursues the same circular course. 



103. The regularity of this circular and successive 

 motion through the cavities of the heart is secured, 

 and any retrograde motion prevented, by the valves 

 which are placed at the principal openings, viz. at the 

 openings of the auricles into the ventricles, and of the 

 ventricles into the pulmonary artery and aorta. 



104. Thus the ring, or venous tendon, which forms the 

 limit of the anterior auricle and ventricle, descending 

 into the latter cavity, becomes these tendinous valves. § 

 These were formerly said to have three apices, and 



* Respecting these openings consult among others J. Abernethy, Philos. 

 Trans. 1798. p. 103. 



f James Penada, Memorie delta Societa Italinna. T. xi. p. 555. 



X Consult Achill. Mieg, Specimen ii. Observationum Botanicarum, &c. 

 Basil. 1776. 4to. p. 12 sq. 



§ Eustachius, Tab. viii. fig. f>. — tab. xvi. fig. 3. Santorini. Tab. Posth. ix. 

 fig. 1. 



F 



