VOL. LXXXVIII.] PHILOSOPHICAL TRANSACTIONS. 287 



tempts to investigate the laws of its operations. How far can we advance in any of 

 the paths which science has opened to us, before we find ourselves enveloped in 

 those thick mists which, on every side, bound the horizon of the human intellect ? 

 But how ample, and how interesting, is the field that is given us to explore! No- 

 body surely, in his sober senses, has ever pretended to understand the mechanism 

 of gravitation; and yet what sublime discoveries was our immortal Newton enabled 

 to make, merely by the investigation of the laws of its action ! The effects pro- 

 duced in the world by the agency of heat, are probably just as extensive, and quite 

 as important, as those which are owing to the tendency of the particles of matter 

 towards each other; and there is no doubt but its operations are, in all cases, deter- 

 mined by laws equally immutable. 



V. Observations on the Foramina Thebesii of the Heart. By Mr. John Abernethy> 



F.R.S. p. 103. 



As the investigation of the resources of nature in the animal economy, for the 

 maintenance of health, and the prevention of disease, cannot but be interesting to 

 the philosopher as well as to the physician, I am therefore induced to submit to the 

 e. s. the following observations. There is a remarkable contrivance in the blood 

 vessels which supply the heart, not to be met with in any other part of the body, 

 and which is of great use in the healthy functions of that organ, but which is par- 

 ticularly serviceable in preventing disease of a part so essential to life. A distended 

 state of the blood vessels must always impede their functions, and consequently be 

 very detrimental to the health of the part which they supply; but as the cavities of 

 the heart are naturally receptacles of blood, a singular opportunity is afforded to its 

 nutrient vessels, to relieve themselves when surcharged, by pouring a part of their 

 contents into those cavities. Such appears to be the use of the foramina by which 

 injections, thrown into the blood vessels of the heart, escape into the cavities of 

 that organ; and which were first noticed by Vieussens, but, being more expressly 

 described by Thebesius, generally bear the name of the latter author. 



Anatomists appear to have been much perplexed concerning these foramina The- 

 besii; even Haller, Senac, and Zinn, were sometimes unable to discover them; 

 which suggested an idea, that when an injection was effused into the cavities of 

 the heart, the vessels were torn, and that it did not escape through natural openings. 

 When these foramina were injected, they were found under various circumstances, 

 as to their size and situation ; and Haller observed, that the injection, for the most 

 part, escaped into the right cavities of the heart. It also remains undetermined, 

 whether these foramina belong both to the arteries and veins, or respectively to- 

 each set of vessels. 



It is from an examination of these openings in diseased subjects, that a solution 

 of such difficulties may probably be obtained. Whoever reflects on the circum- 

 stances under which the principal coronary vein terminates in the right auricle of 

 the heart, will perceive that an impediment to the flow of blood through that vessel 



