614 THE HEART. 



foetus before birth, as well as for a short time after birth 

 till chylification is fully established. 



Another opinion entertained is, that it is a diverticulum 

 of blood from the lungs of the foetus, when" these organs, 

 as before birth, are known to be inactive. 



SECTION III. 

 ORGANS OF CIRCULATION. 



These organs comprise the heart, arteries, and veins, 

 with the lymphatics, which are regarded as appendages. 



Under the head of the vascular tissue will be found a 

 general description of the different systems of circulation ; 

 and under the head of organs of absorption will be seen an 

 account of the lymphatics. All that we propose, therefore, 

 in this place, is to confine our remarks to the heart, and 

 great arterial and venous trunks, by giving somewhat 

 more in detail the description of these important organs. 



THE HEART (Fig. 10.) 



The heart, styled the central organ of the circulation, 

 is a hollow muscle. It is situated (Fig. 196) near the cen- 

 tre of the thoracic cavity, in the middle mediastinum, 

 behind the sternum, in front of the vertebral column, be- 

 tween the lungs, and above the diaphragm. Its form 

 resembles that of a cone, and it is divided into a base, 

 body, and apex. Its direction is oblique, from above, on 

 the right, across the spine, downward and forward to the 

 costal ends of the fifth and sixth cartilages, on the left. 

 Its average length, from apex to base, is estimated at about 

 five inches, four of which are given to the ventricles. The 

 base is about four inches. 



Its weight is from six to eight ounces ; though all these 

 measurements are liable to considerable variation compat- 

 ible with health. 



The heart is surrounded and kept in its position by a 

 fibro-serous membrane, called the pericardium. This mem- 

 brane forms a conical bag for receiving the heart, and, 



