MOVEMENTS OF THE HEART. 



37 



17. Branched 



(Lan ' 



Pulmomc Valves. These valves, also called the semilunar, or sigmoid 

 valves of the right side, are situated at the orifice of the pulmonary artery. 

 They are strong, membranous pouches, with their convex- 

 ities, when closed, looking toward the ventricle. They are 

 attached around the orifice of the pulmonary artery and 

 are applied very nearly to the walls of the vessel when the 

 blood passes in from the ventricle; but at other times 

 their free edges meet in the centre, opposing the regurgi- 

 tation of blood. At the centre of the free edge of each 

 valve is a little corpuscle called the corpuscle of Arantius ; 

 and just above the margins of attachment of the valves, 

 the artery presents three little dilatations, or sinuses, called 

 the sinuses of Valsalva. The corpuscles of Arantius prob- FlG 

 ably aid in the adaptation of the valves to each other and 

 in the effectual closure of the orifice. 



Mitral Valve. This valve, sometimes called the bicus- 

 pid, is situated at the left auriculo-ventricular orifice. It is called mitral 

 from its resemblance, when open, to a bishop's mitre. It is attached to the 

 edges of the auriculo-ventricular opening, and its free borders are held in 



place, when closed, by 

 the chordae tendineae of 

 the left side. It presents 

 no material difference 

 from the tricuspid valve, 

 with the exception that it 

 is divided into two cur- 

 tains instead of three. 



Aortic Valves. These 

 valves, also called the sem- 

 ilunar, or sigmoid valves 

 of the left side, present 

 no difference from the 

 valves at the orifice of 



FIG. 18. Valves of the heart (Bonamy and Beau). the pulmonary artery. 



1, right auriculo-ventricular orifice, closed by the tricuspid valve ; rpn + , j 4/u^ 



2, fibrinous ring ; 3, left auriculo-ventricular orifice, closed by 1 hey are Situated at tne 



the mitral valve ; 4, fibrinous ring ; 5, aortic orifice arid valves ; + ^fl 

 6, pulmonic orifice and valves ; 7, 8, 9, muscular fibres. ^ y< 



MOVEMENTS OF THE HEART. 



The dilatation of the cavities of the heart is called the diastole, and the 

 contraction of the heart, the systole. When these terms are used without any 

 qualification, they are understood as referring to the ventricles ; but they are 

 also applied to the action of the auricles, as the auricular diastole and systole, 

 which are distinct from the action of the ventricles. 



A complete revolution of the heart consists in the filling and emptying of 

 all its cavities, during which they present an alternation of repose and activity. 

 As these phenomena occupy, in many warm-blooded animals, a period of time 



7- 



