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The blood is made to circulate within the system of closed tubes in which it is contained by means of the alternate contraction and relaxation of the heart.

Blood Circulation

The blood is made to circulate within the system of closed tubes in which it is contained by means of…

Diagram showing the compartments of the heart. The smaller compartments are the auricles (also known as atria) and the larger compartments are the ventricles. The middle part of the figure represents the heart with its two sides; <em>a</em> being the right auricle, <em>b</em> the right ventricle, <em>d</em> the left auricle, and <em>e</em> the left ventricle. The blood is received in the right auricle, <em>a</em>, from the general system, <em>f</em>. It then passes into the right ventricle, <em>b</em>, and is forced by the contraction of it through arteries to the lungs, <em>c</em>. From the lungs it comes back to the heart, to the left side, and enters the left auricle, <em>d</em>. From this it passes into the left ventricle, <em>e</em>, from which it is sent all over the body, represented by <em>f</em>.

Heart, Compartments of

Diagram showing the compartments of the heart. The smaller compartments are the auricles (also known…

Transverse section through the middle of the ventricles (right and left) of a dog's heart in diastole (top) and in systole (bottom).

Transverse Section through the Ventricle of a Dog's Heart

Transverse section through the middle of the ventricles (right and left) of a dog's heart in diastole…