PERICARDIUM. HEART. 531 



It consists, therefore, of two layers, an external fibrous and an in- 

 ternal serous. The fibrous layer is attached, above, to the great 

 vessels at the root of the heart, where it is continuous with the tho- 

 racic fascia ; and below, to the tendinous portion of the diaphragm. 

 The serous membrane invests the heart with the commencement of its 

 great vessels, and is then reflected upon the internal surface of the 

 fibrous layer. 



The HEART is placed obliquely in the chest, the base being directed 

 upwards and backwards towards the right shoulder ; the apex forwards 

 and to the left, pointing to the space between the fifth and sixth ribs, 

 at about two or three inches from the sternum. Its under side is flat- 

 tened, and rests upon the tendinous portion of the diaphragm ; its 

 upper side is rounded and convex, and formed principally by the right 

 ventricle, and partly by the left. Surmounting the ventricles are the 

 corresponding auricles, whose auricular appendages are directed for- 

 wards, and slightly overlap the root of the pulmonary artery. The 

 pulmonary artery is the large anterior vessel at the root of the heart ; 

 it crosses obliquely the commencement of the aorta. The heart con- 

 sists of two auricles and two ventricles, which are respectively named, 

 from their position, right and left. The right is the venous side of 

 the heart ; it receives into its auricle the venous blood from every part 

 of the body, by the superior and inferior cava and coronary vein. 

 From the auricle the blood passes into the ventricle, and from the 

 ventricle through the pulmonary artery, to the capillaries of the lungs. 

 From these it is returned as arterial blood to the left auricle ; from 

 the left auricle it passes into the left ventricle ; and from the left ven- 

 tricle is carried through the aorta, to be distributed to every part of 

 the body, and again returned to the heart by the veins. This consti- 

 tutes the course of the adult circulation. 



The heart is best studied in situ. If, however, it be removed from 

 the body, it should be placed in the position indicated in the above 

 description of its situation. A transverse incision should then be 

 made along the ventricular margin of the right auricle, from the ap- 

 pendix to its right border, and crossed by a perpendicular incision, 

 carried from the side of the superior to the inferior cava. The blood 

 must then be removed. Some fine specimens of white fibrin are fre- 

 quently found with the coagula ; occasionally they are yellow and 

 gelatinous. This appearance deceived the older anatomists, who 

 called these substances " polypus of the heart : " they are also fre- 

 quently found in the right ventricle, and sometimes in the left cavities. 



The RIGHT AURICLE is larger than the left, and is divided into a 

 principal cavity or sinus, and an appendix auriculae. The interior of 

 the sinus presents for examination five openings ; two valves ; two 

 relicts of foetal structure ; and two peculiarities in the proper structure 

 of the auricle. They may be thus arranged : - 



