HEART 403 



auricles into the ventricles. They are firmly held down in 

 the ventricular cavity by the chordas tendinete. When the 

 ventricles contract, the papillary muscles pull the cusps of 

 the valves together and thus occlude the opening between 

 auricles and ventricles. The cusps are further pressed face 

 to face by the increasing pressure in the ventricles, and they 

 may become convex towards the auricles. They thus form 

 a central core around and upon which the ventricles 

 contract. 



On the left side of the heart, the strong anterior cusp of 

 the mitral valve does not materially shift its position. Ii 

 may be somewhat pulled backwards and to the left. The 

 posterior cusp is pulled forwards against the anterior. 



On the right side, the infundibular cusp of the tricuspid 



174. — State of the various parts of the Heart throughout the Cardiac 

 Cj'cle. 1, auricular s3-stole ; 2, beginning of ventricular systole (latent 

 period) ; .S, period of outflow from the ventricle ; 4, period of residual 

 contraction ; .5, beginning of ventricular diastole. 



valve is stretched between the superior and inferior papillary 

 muscles, and is tluis pulled towards the bulging septum, 

 against which it is pressed by the increasing pressure inside 

 the ventricles. The posterior cusp has its anterior margin 

 pulled forward and its posterior margin backwards, and is 

 thus also pulled toward the septum. The septal cusp remains 

 against the septum. The greater the pressure in the 

 ventricle, the more firmly are the two outer cusps pressed 

 against the septum, and the more completely is the orifice 

 between the auricle and the ventricle closed. On the risrht 

 side of the heart other factors play an important part in 

 occluding the orifice ; the muscular fibres which surround 

 the auriculo-ventricular opening contract, and the papillary 

 muscles pull the auriculo-ventricular ring downwards and 

 inwards by means of the chordae which are inserted into it. 



