1870.] 



four Orifices of the Heart. 



267 



The mean areas of the four orifices thus obtained are found to be 

 as follows : — 



Males. Females. 



Tricuspid 1*78 sq. in. 1*6 sq. in. 



Pulmonic 1 *97 



Mitral 1-27 1*27 



Aortic *78 '67 



Or, for facility of recollection, we may consider the respective mean areas 

 in the male to be : — 



Tricuspid 1| sq. in. 



Pulmonic 1 



Mitral 1J 



xiortic | 



whence it is obvious that the apertures differ very considerably in area 

 from each other, the tricuspid having the largest area, its orifice being 

 more than double the size of the aortic opening. 



Irregular, however, as these areas may appear to be in magnitude with 

 respect to each other, we shall find, on pushing our observations further, 

 that there is a distinct and constant law presiding over them, and this law 

 is discovered when we compare the ratios of the areas of corresponding 

 orifices. Thus, 



Area of tricuspid_l , 7S_ , . , 

 "Area of mitral ~~¥27~ ' Y 



Area of pulmonic = 1 near j r 



Area of aortic '78 



or, in other words, the area of the tricuspid appears from these calculations 

 to bear nearly the same relation to the area of the mitral which the area of 

 the pulmonic does to that of the aortic orifice, i. e. were the tricuspid, for 

 example, twice the size of the mitral orifice in area, the pulmonic would be 

 twice the size of the aortic orifice in area, the two ratios differing from 

 each other only by one-tenth. 



Again, if we adopt Dr. Reid's measurements of the circumference of the 

 healthy cardiac orifices (these measurements being given in Dr. Peacock's 

 work), we shall find this law to be more conclusively proved. 



According to Dr. Reid the measurements of the circumferences are as 

 follows : — 



Male. Female. 



Tricuspid 5*3 in. 4*9 in. 



Pulmonic 37 3*5 



Mitral 4*6 4*2 



Aortic 3*2 3 



