THE LEFT AURICLE 245 



with one another at their bases, and their free margins and 

 ventricular surfaces give attachment to the chordae tendinese. 

 Their central part is thick and strong, the lateral margins 

 thinner and flexible. 



4. The chorda* tcndinrce are attached as follows: several to the 

 attached margin of each flap, blending with the fibrous ring; 

 several to the strong central part; and the finest and most 

 numerous to the margins, of each curtain. 



5. The columnce carnece are projecting bundles of muscular 

 substance found all over the ventricular wall excepting the 

 conus arteriosus. They are of three classes: the first are mere 

 ridges, attached by one side and both extremities; the second 

 are attached only by both extremities; the third (musculi 

 papillares) are two in number, an anterior and a posterior, 

 attached by only one extremity, the free end having chorda 1 

 tendinese attached to it. 



6. The three semilunar valves guard the pulmonary orifice. 

 They are semicircular, their free margins being thick and ten- 

 dinous and presenting at the middle a small fibrous nodule, the 

 corpus Arantii. On each side of this body, just behind the free 

 margin, the valve presents a small thinned-out interval, and 

 when the valves are closed during diastole these valves (lunulce) 

 are in contact, and so also are the three nodules. These latter 

 prevent any leakage from the triangular space which would 

 otherwise be left. 



7. At the commencement of the pulmonary artery are three 

 pouches, the sinuses of Valsaha, placed one behind each valve. 

 They resemble those of the aorta, but are smaller. 



THE LEFT AURICLE 



The left auricle is smaller and thicker walled than the right, 

 and consists, like the right, of a sinus and an appendix. The 

 latter overlaps the pulmonary artery. Within it presents the 

 following features of interest: 



The orifices of the pulmonary wins, opening two into the right 

 and two into the left side; the auriculoventricular orifice; and 

 a few musculi pectinati on the inner side of the appendix. 



