Chap. 23-1 [ 2 37 1 



CHAP. XXIII. 



THE HEART. 



The Pericardium. The Heart. The Ventricles and Auricles. Their 

 TJ/l'j. General View of the Blood-<veJ/els. 



E heart is a hollow mufcle, included in a 

 JL membranous bag, called the pericardium. 



This membrane inclofes not only the heart, but 

 the great veflels which arife from it. This covering 

 of the heart confifts of three laminas; the external of 

 thefe is formed by a duplicature of the mediaflinum. 

 The middle lamina, which is the thickeft and ftrongeft, 

 is compofed of very fine tendinous fibres, which at 

 the lower part are connected and mixed with thofe of 

 the diaphragm. The internal lamina feems to be a 

 continuation of the outer coat of the heart and great 

 veffels. Within the pericardium is found a quantity 

 of tranfparent liquor, which facilitates the motions of 

 the heart, by preventing friction. 



The heart is placed in man almoft tranfverfely, 

 and reds on the diaphragm at the anterior part of the 

 thorax. The bafe or broad part of rhe heart is di- 

 refted towards the right fide, its point or apex towards 

 the left, and this latter is fo placed, as when the heart 

 beats to ftrike the fixth rib. The upper furface'of 

 the heart is convex -, the lower, which refts on the 

 diaphragm, is flat. The greater part of the heart lies 

 in the left cavity of the thorax. 



The fubflance of the heart is mufcular, and 'is 

 compofed of fibres, which, arifing from the bafe, where 

 it is tendinous, take a winding courfe towards its apex 

 in various diredions. 



The 



