PECULIARITIES OF THE FCETUS. 273 



the subsequent periods of life, this equilibrium, in the force and 

 time of their contraction, remains uniform : a circumstance 

 proved, conclusively, by the. health and strength of adults in 

 whom the valve has never adhered to the day of their d<ath; 

 an observation made by many anatomists, and of which I have 

 witnessed several examples. In one of them I passed two fin- 

 gers readily from one auricle into the other, owing to the un- 

 usual size of the aperture. 



The valve which closes the foramen ovale is, first of all, 

 scarcely perceptible ; but as the foetus advances in age, it also 

 advances in size, and is, indeed, large enough to close the fora- 

 men some weeks before birth. It is formed from the lining 

 membrane of the two auricles, with some intermediate sub- 

 stance. 



The Valve of Eustachius, which exists also in the adult heart, 

 is placed at the anterior semi-circumference of the orifice of 

 the ascending vena cava in the right auricle, one of its ends ad- 

 hering to the anterior margin of the foramen ovale. This valve, 

 contrary to the one in the foramen ovale, is larger in proportion 

 as the foetus is younger, and, when first observed, covers the 

 whole orifice of the vena cava ascendens ; its opening, however, 

 is in the direction of the current of blood in the latter. It also is 

 formed by a duplicature of the lining membrane of the auricle; 

 and, from its disposition, determines the blood of the ascending 

 cava to flow through the foramen ovale into the left auricle, 

 either wholly or in part, according to the period of gestation, 

 Its obliquity also gives a direction to the blood of the descend- 

 ing cava, into the right ventricle from the right auricle. These 

 uses of the Eustachian valve were pointed out by the celebrated 

 Sabatier:* their value will be illustrated hereafter. 



The ventricles of the Heart, at birth, have the same struc- 

 ture and internal arrangement as afterwards; they are remark- 

 ble, however, for being of equal thickness, or nearly so, an ob- 

 servation of Mr. John Hunter. t This fact is connected with 

 the circumstance of their both contributing to the aortic cir- 

 culation till respiration begins, owing to the pulmonary artery 



* Traitg d'Anat. vol. ii. p. 296, f Animal (Economy, 



