NOTE ON THE CONFIGURATION OF THE HEART. 75 



generally described as posterior. As already mentioned, it is 

 distinctly flattened, and looks almost directly doivnwards. 



This surface is triangular in outline, and I have called it 

 basal, because it is that part of the heart which fits into and 

 fills up the eoGiJanded basal part of the 'pericardium, where the 

 latter is attached to the diaphragm. The basal surface of the 

 heart is separated from the anterior surface by the margo 

 obtusus and margo acutus, and from the posterior surface by 

 the posterior border. 



3. The posterior or auricular surface. This includes the back 

 of the auricles. It looks directly backwards, and opening into 

 it are the inferior and superior cava, and the right and left 

 pulmonary veins. It is separated from the other surfaces 

 by the borders already mentioned. 



In the quadrupeds which I dissected, I found that the 

 posterior and basal surfaces were not distinctly marked off 

 from each other. 



From the above description of the human heart, it seems that 

 there is a close correspondence in shape between the fibrous 

 pericardial sac and the heart which it contains. The peri- 

 cardium is a somewhat triangular-shaped cavity, broad and 

 expanded below where it is attached to the diaphragm, and 

 narrowed considerably above where it blends gradually with 

 the sheaths of the great vessels which spring from the heart 

 (Plate VI. figs. A. + B.). Likewise, the heart is broad and 

 expanded below where it rests on the diaphragm (the peri- 

 cardium intervening). This part of the organ includes the 

 inferior or basal surface, the lower part of the posterior surface, 

 the intervening borders together with the ventricular apex 

 (Plate IV. fig. B., and Plate VI. fig. C). 



The upper part of the heart where the great vessels arise 

 (part of the ' so-called base ') becomes narrowed like the peri- 

 cardium. 



It appears that the part of the heart which has hitherto been 

 termed the ' base,' seems to be a rather indefinite portion both 

 in position and extent. I found, however, that in hearts 

 hardened with formalin, the posterior surface, which is generally 

 distinct, includes the greater part of the ' base.' It is evident 

 that from the shape and position of the formalin heart, a more 



