THE HEART. 



101 



Columns Carnea, muscular columns projecting from the surface of the ven- 

 tricle, of which 3 or 4, called Columntz Papillares, give attachment to the 

 chordae tendinae. 



Semilunar Valves, are 3 in number, and guard the orifice of the pulmonary 

 artery, each about the middle of its free margin has a fibro-cartilaginous 

 nodule, the Corpus Arantii, which more perfectly closes the orifice. 

 Opening of the Pulmonary Artery, at the superior and internal angle of the 

 ventricle, the Conus Arteriosus. It is circular in form, surrounded by a 

 fibrous ring, and is guarded by the semilunar valves. 

 Sinuses of Valsalva, are 3 pouches, one behind each valve, between it and 



the commencement of the pulmonary artery. 



Describe the Left Auricle. Its walls are about \y z lines in thickness, 

 its capacity rather less than 2 fluidounces, has an appendix auriculae, and 

 receives the arterialized blood from the lungs. It presents the following in- 

 ternally : 



Openings of the Pulmonary Veins, are 4 in number, sometimes 3, as the two 



left veins frequently end in a common opening. 

 Left Auricula-ventricular Opening, is smaller than the right one. 

 Musculi Pectinati, on the inner surface of the appendix. 

 Depression, corresponding to the fossa ovalis in the right auricle. 

 Describe the Left Ventricle. 

 It is longer, thicker, and more coni- 

 cal than the right, projecting towards 

 the posterior aspect. Its walls are 

 the thickest of those in the heart, 

 being twice as thick as those of the 

 right ventricle. Its interior presents 

 the following : 



Aortic Opening, is small and cir- 

 cular, placed in front and to 

 the right of the auriculo-ven- 

 tricular, a segment of the mitral 

 valve being between them. It 

 is surrounded by a fibrous ring, 

 and guarded by semilunar 

 valves. 



Mitral Valvef consists of two 

 unequal-sized segments, and is 

 attached to the fibrous ring which surrounds the auriculo-ventricular 

 opening. Its margins are connected with the ventricular walls by Chorda 

 Tendin&d and Musculi Papillares. 

 9* 



