Dissection of Sheeph Heart. 169 



valve which projects into the cavity of the Ventricle : near 

 its attachment to the Heart this valve is undivided, but it pre- 

 sents three chief points at its lower margin, and is thence 

 named the Tricuspid Valve ; to the free margin of this valve 

 are attached the small tendinous cords, Chordoe Tendinece, 

 above mentioned. 



During the contraction of the Yentricle the valve is raised 

 by the blood, so as to close the opening into the Auricle ; but 

 the further protrusion of it into the auricular cavity is arrested 

 by the small tendinous cords. 



From the funnel- sHaped part of the right Yentricle the 

 pulmonary artery arises ; at its mouth are seen three Semi- 

 lunar or Sigmoid valves : these should be further brought to 

 view by prolonging the incision in the anterior wall of the 

 Ventricle upwards, into the pulmonary artery, between two of 

 the segments of these valves. In the free margin of each 

 valve there is seen a slightly thickened nodule called the 

 Corpus Arantii; and in the wall of the artery, within each 

 valve, and on a level with the free margin, is seen a slight 

 hollow, called the Sitius of Valsalva* 



When the blood is entering the artery these valves are 

 pressed against the wall ; but when the distended artery re- 

 acts upon the contained blood, the valves are thrown towards 

 towards the centre of the cylinder and arrest the return of the 

 blood to the Ventricle. 



Dissection of Left Auricle. A cut should be made with 

 the scissors from the entrance of the right pair of pulmonary 

 veins {i.e. just above and to the left of the fossa ovalis) to the 

 free extremity of the Auricle. 



The Musculi Pectinati, and the Auriculo-ventricular orifice 

 will be seen to resemble those in the other Auricle : and on 

 holding the septum between the Auricles to the light, a slight 



* These are better marked in the Aorta. 



