BOOK VIII. 



PART II. 



Of the Special Anatomy of the Circulatory System, 



CHAPTER I. 



OF THE HEART AND PERICARDIUM. 



THE Heart, (Cor,) the centre of the circulation, is situated 

 in the thorax, between the sternum and the spine; being bound- 

 ed on its sides by the lungs, and below by the tendinous centre 

 of the diaphragm. It is a hollow muscular organ. 



The heart is of a conoidal shape, but flattened on the surface 

 which lies upon the diaphragm. This flat surface is on a hori- 

 zontal line with the lower end of the second bone of the ster- 

 num ; the base of the cone is towards the vertebrae, and looks 

 obliquely backwards to the right side, while the apex is about 

 the junction of the left fifth rib with its cartilage. Its common 

 weight is about six ounces. Its greatest length, to wit, that 

 from the apex to the base, is about five and a half inches, four 

 of which are taken up by the ventricles: its base is about three 

 and a half inches in .diameter. 



The heart is divided into four cavities; two auricles and two 

 ventricles: the places where the partitions are placed between 

 these cavities are marked on the surface of the heart by fis- 

 sures, sufficiently distinct to be immediately recognised. The 

 two auricles form the base of the heart, the ventricles con- 

 stitute its body, and the anterior end of the left ventricle, 

 by being extended somewhat beyond the right forms the 



