ANATOMY OF THE HEART. 



39 



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 probably aid in the adapta- 

 tion of the valves to each other and 

 in the effectual closure of the orifice. 



Mitral Valve. This valve, some- 

 times called the bicuspid, is situated 

 at the left auriculo-ventricular orifice. 

 It is called mitral from its resem- 

 blance, when open, to a bishop's mi- 

 tre. It is attached to the edges of the 

 opening, and its free borders are held 

 in place, when closed, by the chords 

 tendineas of the left side. It presents 

 no material difference from the tri- 

 cuspid valve, with the exception that 

 it is divided into two curtains instead 

 of three. 



Aortic Valves. These valves, also 

 called the semilunar or sigrnoid valves 

 of the left side, present no difference 

 from the valves at the orifice of the 

 pulmonary artery. They are situated 

 at the aortic orifice. 



The physiological anatomy of the 

 tricuspid and mitral valves may be 

 studied by cutting away the auricles 

 so as to expose the auriculo-ventric- 

 ular openings, introducing a pipe into 

 the pulmonary artery and aorta, after 

 destroying the semilunar valves, and 

 then forcing water into the ventricles 



by a syringe or from a hydrant. In this way the play of the valves may be strikingly 

 exhibited. 



We can study the action of the semilunar valves by cutting away enough of the ven- 

 tricles to expose them and forcing water into the vessels. These experiments give an 



Fro. 15. Muscular fibres of the ventricles. (Bonamy and Beau.) 

 1, superficial fibres, common to both ventricles ; 2, fibres of the 

 left ventricle ; 3, deep fibres, passing upward toward the 

 base of the heart ; 4, fibres penetrating the left ventricle. 



FIG. 16. Anastomosing muscular fibres of the heart. (Morel.) 



idea of -the immense strength of the valves ; for they can hardly be ruptured by a force 

 which is not sufficient to rupture the vessels themselves. 



