FUNCTION OF THE VALVES. 103 



dotted ones the edges of the valves, firstly, when the valves 

 are in contact with the walls (A), and, secondly, when the 

 walls being dilated, the valves are drawn away from them (B). 

 This position of the valves and arterial walls is retained so 

 long as the ventricle continues in contraction ; but, so soon as 

 it relaxes, and the dilated arterial walls can recoil by their 

 elasticity, they press the blood as well towards the ventricles 

 as onwards in the course of the circulation. Part of the blood 

 thus pressed back lies in the pouches (a, Fig. 37, B) between 

 the valves and the arterial walls ; and the valves are by it 

 pressed together till their thin lunated margins meet in three 

 lines radiating from the centre to the circumference of the 

 artery (7 and 8, Fig. 38). 



FIG. 38. 



View of the base of the ventricular part of the heart, showing the relative position 

 of the arterial and auriculo-ventricular orifices. %. The muscular fibres of the 

 ventricles are exposed by the removal of the pericardium, fat, bloodvessels, &c. ; the 

 pulmonary artery and aorta have been removed by a section made immediately 

 beyond the attachment of the semilunar valves, and the auricles have been removed 

 immediately above the auriculo-ventricular orifices. The semilunar and auriculo- 

 ventricular valves are in the nearly closed condition. 1, 1, the base of the right 

 ventricle ; 1', the conus arteriosus ; 2, 2, the base of the left ventricle ; 3, 3, the divided 

 wall of the right auricle ; 4, that of the left ; 5, 5', 5", the tricuspid valve ; 6, 6', the 

 mitral valve. In the angles between these segments are seen the smaller fringes 

 frequently observed ; 7, the anterior part of the pulmonary artery ; 8, placed upon 

 the posterior part of the root of the aorta ; 9,. the rig'ht, 9', the left coronary artery. 

 (From Quain's Anatomy.) 



Mr. Savory has clearly shown that this pressure of the blood 

 is not entirely sustained by the valves alone, but in part by 



