DESCRIPTION OF THE HEART. 635 



from the centre at angles of 120. The free and attached margins of 

 each valve contain tendinous fibres ; tendinous fibres also radiate 

 across the valve, from the corpus Arantii to its attached margins, so 

 that two thin semilunar portions, called lunulce, are left, one on either 



Fig. 106. 



Fig. 106. Three views of the base of the heart, .after removal of the auricles; the commencements of the 

 pulmonary artery and the aorta are left, in order to show the valves of the heart and their altered posi- 

 tions at different moments of the heart's action, a, 1, interior of part of the right auricle ; 2. right auric- 

 ulo-ventricular, or tricuspid valve; 3, right ventricle; 4, pulmonary artery and its semilunar valves; 



5, interior of part of the left auricle; 6, left auriculo-ventricular, bicuspid, or mitral valve; 7, left ventri- 

 cle ; 8, aorta, and its semilunar valves. In this view, all the valves have their segments a little apart. 



6, shows the auriculo-ventricular apertures open, and their valves apart; the arterial orifices are closed, 

 and their valves in contact: condition during diastole of the ventricles, c, shows the opposite conditions 

 of the valves ; condition during systole of the ventricles. 



side of the nodule. Behind the segments, the pulmonary artery pre- 

 sents, at its base, three slight dilatations or pouches, the sinuses of 

 Vahalva. 



The left auricle (Fig. 105, 7), somewhat smaller than the right, has 

 thicker walls, measuring, on an average, 1J line in thickness, whilst 

 those of the right auricle measure only 1 line. Like the latter, it con- 

 sists of a sinus and an appendix. The sinus is placed behind the 

 aorta and pulmonary artery. The appendix, projecting forwards and 

 to the left side, is narrower, and more curved and notched, than the 

 right one ; its musculi pectinati are smaller and less numerous. At 

 the back of the auricle are the openings of the four pulmonary veins, two 

 on each side, their orifices being destitute of valves. On the septum, 

 between this and the right auricle, is a lunated depression, bounded 

 below by a crescentic ridge, the vestige of the foramen ovale. At the 

 lower part of the auricle is the opening into the left ventricle, or left 

 auriculo-ventricular opening. 



The left ventricle, 8, is longer, and more conical in shape, than the 

 right ventricle ; it has much thicker walls, the proportion being as 3 

 to 1. The walls are thickest opposite the middle of the cavity, and 

 thinnest at the apex, whilst the right ventricle is thickest near its base. 

 The average thickness, in lines, of the walls of the two ventricles in 

 the male, in whom they are somewhat thicker than in the female, are, / 

 for the left ventricle, at the base, middle, and apex, 4J, 5^, and 3f ; 

 and for the right, 1 J f , If, and 1^ (Bizot). The left ventricle increases 



