CIRCULATION OF THE BLOOD 



contents of the cavities, especially the ventricles, with each systole (see 

 Plate II, Fig. 3). 



The distribution of the nerves to the heart and the arrangement 

 of the ganglia and nerve-terminations in its substance will be de- 

 scribed in connection with the influence of the nervous system on the 

 circulation. 



Each ventricle has two orifices, one by which it receives blood from 

 the auricle, and the other by which the blood passes from the right side 

 to the lungs and from the left side to the general system. All these 

 openings are provided with valves, which are so arranged as to allow 

 the blood to flow in but one direction. 



Tricuspid Valve. This valve is situated at the right auriculo-ven- 

 tricular opening. It has three curtains, formed of a thin but resisting 



membrane, which are at- 



7 ^ tached around the open- 



ing. Their free borders 

 are attached to the chordae 

 tendineae. 



The Pulmonic Valves. 

 The three pulmonic 

 valves, also called the 

 semilunar or the sigmoid 

 valves of the right side, 

 are situated at the orifice 

 of the pulmonary artery. 

 They are strong mem- 

 branous pouches, with 

 their convexities, when 



Fig. 22. Valves of the heart (Bonamy and Beau). 



i, right auriculo-ventricular opening, closed by the tricuspid 

 valve ; 2, left auriculo-ventricular opening, closed by the mitral closed, looking toward the 

 valve; 4, fibrous ring; 5, aortic opening and valves ; 6, pul- ven t n >lp Thev arf> at 

 monic opening and valves ; 8, 9, muscular fibres. 



tached to the borders of 



the orifice of the pulmonary artery, and when closed, their free edges 

 meet and prevent regurgitation of blood. At the centre of the free 

 border of each valve is a little body called the corpuscle of Arantius. 

 Just above the attached margins of the valves, the vessel presents three 

 dilatations, or sinuses, called sinuses of Valsalva. The corpuscles of 

 Arantius aid in the close adaptation of the free borders of the valves to 

 each other to prevent regurgitation of blood. 



Mitral Valve. - The mitral valve, sometimes called the bicuspid, is 

 situated at the left auriculo-ventricular orifice. It is attached to the bor- 

 ders of this opening, and its free margins are held in place, when the 

 valve is closed, by the chordae tendineae, to which they are attached. It 



