STRUCTURE OF THE HEART. 79 



. Few people, I suspect, imagine that they 

 have, to all intents and purposes, a couple of hearts. 



j) r . B. If we were to judge by the frequency with 

 which they lose them, they ought to have a score. Let 

 me now call your attention to the human heart. 



The double heart of man is situated in the lower and 

 front part of the chest and a little to the left side. It is 

 of an irregular, pyramidal shape, with its base upwards 

 and its apex pointing obliquely downwards, and is en- 

 closed in a membranous bag called the pericardium, 

 which fixes it in its place, and protects it from the con- 

 tact of other organs. Being double it is generally dis- 

 tinguished into the left and right hearts, or, to use names 

 which at the same time give an idea of the relative 

 office of these parts, arterial and venous hearts. Neither of 

 these hearts is formed by a single cavity, but each is com- 

 posed of two cavities. The larger is called the ven- 

 triele ; the smaller is merely an appendage to the other, 

 and is called the auricle. The walls of the ventricle 

 are exceedingly thick and strong. Their internal sur- 

 face is very irregular, owing to numerous little, fleshy 

 columns, which run in the direction of the length of the 

 ventricle, in bass releif. They are endowed with great 

 contractile power, and act with immense force in bring- 

 ing together the sides of the ventricle. Each ventricle 

 presents two apertures one by which the blood is ad- 

 mitted into it, and the other by which it is sent out. 

 The auricle is much smaller than the ventricle, the sides 

 are thinner, and its fleshy columns are less powerful. 

 Now, we will follow the blood in its course through the 

 hearts, and you will see some curious contrivances by 

 means of which they exert a force on the motion of the 

 blood. 



First, let us trace it through the venous heart. The 

 venous blood, after being brought from every portion of 

 the body, is at last collected into two great veins, the 

 one ascending through the abdomen with the blood of 

 the lower parts of the body, called the vena cava inferi- 



