000 PHILOSOPHICAL TRANSACTIONS. [aNNO 17 10. 



over all that part which is cut on the basis of the heart : for then it is easy to 

 view all the internal parts of the heart, and observe that there is but one only 

 ventricle, which comprehends the whole extent of the heart, and is as uniform 

 and plain as either of the ventricles of the human heart, or of any other animal 

 whatever; and that it is impossible to remark any kind of septum, either mus- 

 culous or membranous, that might make any division or cellule in this ventri- 

 cle : so that it is very surprising, that the anatomists of the Royal Academy of 

 Paris should have shown, the one three, and the other four ventricles, in the 

 heart of a land tortoise of America. 



After having considered the extent of the cavity of the heart, there remain 

 two things to be examined. The first is, that in its back part there are five 

 holes or orifices, two of which are on the left side : these are the orifices of the 

 two funnels of the auricles : they are covered by a large valve lying flat upon 

 them, supported in its middle by the prolongation of the septum, which divides 

 the auricles, in such a manner, that half of it covers the orifice of the right 

 auricle, and the other half that of the left ; so that this valve resembles two 

 folding doors of a porch, which have the same support, the one opening or 

 shutting to the right, and the other to the left. It is plain that this valve per- 

 mits the entrance of the blood into the ventricle of the heart, but opposes its 

 return into the auricles ; because this blood being once in the heart, presses by 

 its own weight on this double valve, and keeps it close and flat upon these 

 orifices : which confirms perfectly well the office of the valve, in the foramen 

 ovale in the hearjt of a human foetus, the disposition being entirely the same. 

 The other three holes, lying on the right side of the ventricle of the heart, are 

 the orifices of the four arteries which come out of the basis : of these three 

 holes, that which is most to the left, is the orifice of the pulmonary artery ; the 

 highest, the orifice of the aorta sinistra descendens ; and that most to the right 

 side, is common to the arteria aorta dextra, and to the superior aorta. Each 

 of these orifices is furnished with two semilunary valves, which permit the blood 

 to pass without difficulty from the ventricle of the heart into the arteries, but 

 hinder its return into the heart. It is a mere illusion to place these holes in 

 diflferent ventricles; they are all in one and the same cavity; so that the blood 

 enters into this only cavity by the two holes which are on the left side, and goes 

 out of this same ventricle, by the three holes which are on the right side. 



The second thing remarkable in this ventricle, is the fibres of the heart. 

 They are of two sorts ; some are external, disposed under the common mem- 

 brane in several planes, very small, but obliquely circular, extending from the 

 basis, but particularly about the arteries, which serve them instead of tendons. 



