120 



ANIMAL PHYSIOLOGY. 



rushing out of the ventricles ; but as soon as the ventricular 

 contraction ceases, and the elasticity of the arteries tends to 



make the blood recoil, 

 they are filled with the 

 blood in the arteries, the 

 sides of each are pressed 

 against the adjacent sides 

 of the two others, and all 

 three reach in to the centre 

 of the orifice, so as effectu- 

 ally to block it up. The 

 action of these valves can 

 be studied in a sheep's 

 heart, by pouring water 

 into the cut arteries, when 

 it will be seen that not a 

 drop passes back into the 

 ventricles. 



The auriculo-ventricular 

 valves of the right and 

 left sides of the heart are 

 named respectively the 

 tricuspid and the bicuspid 

 Fig. 60. LEFT SIDE OF THE HEART, or mitral, the one consist- 

 The pulmonary artery has been re- ing of three p ointed mem . 

 moved. An arrow is passed through , *- 



the aortic orifice between the semi- branous flaps or cusps, and 

 lunar pouches of its valve; and the the other of two. The 

 lower end of the arrow rests on the cusps are attached at the 

 anterior cusp of the mitral valve. base to tlie marg i ns O f the 

 a, b. Anterior and posterior muscuh , . i 



papillares, with chorda* tendmese aunculo- ventricular ^ on- 

 passing up from each to both cusps; fices, and are kept in the 

 c, auricular cavity. interior of the ventricles 



by a number of threads, chordce tendinece, attached to 

 their edges and backs, and fastened at the other end to 

 muscular prominences, the musculi papillares. The arrange- 

 ments are on the same principle in both valves, but may be 

 studied best on the mitral, which is the more perfect of the 

 two. The chords tendineaD of each cusp are divided into 

 two sets ; those from each half joining with those of the 

 adjacent half of the other cusp to be inserted into one mus- 



