392 ANGIOLOGT. 



infundibulum, whose smooth inner surface is destitute of carneae- 

 columnae. The entrance of the pulmonary artery is guarded by 

 three semilunar or sigmoid valves, which consist of semicircular 

 folds of the lining membrane ; they are almost transparent, and 

 attached by their convex margins to the tendinous ring which 

 surrounds the origin of the artery. Their free edges are almost 

 straight, and thinner than the attached ones, each presenting a 

 mesian fibro-cartilaginous nodule, the corpus Arantii. 



When blood passes from the ventricle to the pulmonary artery, 

 tlie valves are laid against the sides of the vessel; when the 

 current is checked, a portion of it falls back towards the ventricle, 

 and the valves are now thrown inwards ; they become distended, 

 overlap, and completely close the tube. Wben the valves are 

 shut, the surfaces next the vessel are concave, the ventricular ones 

 convex. 



The corpora Arantii are said to fill up the small space that 

 would otherwise be left in the axis of the canal by the meeting 

 of the circular valves ; but these bodies are frequently indistinct 

 in the pulmonary artery, and rarely project beyond the free 

 margins of the valves. Behind the valves, at the commencement 

 of the artery, are three dilations or pouches, bounded below by 

 the valves themselves, and called the sinuses of Valsalva. 



From the inner surface of the ventricular walls project the 

 fleshy columns, or carneoe columnce. They are of three kinds, 

 attached by their external surface and extremities, their internal 

 surfaces being free, forming prominent ridges, sometimes dividing 

 and subdividing. One variety, three or four in number, terminate 

 in short blunt processes, and constitute the musculi papillares, 

 whence the chordae tendinese spring. These carneae columnae 

 form an intricate network on the inner surface of the ventricle, 

 occasionally crossing the cavity, and forming what are called the 

 moderator bands. A very well developed one crosses the middle 

 of the cavity from the interventricular septum to the outer wall ; 

 this is termed the great moderator hand, and is said to be 

 especially well marked in " running " animals. 



LEFT AURICLE. 



The blood, after being purified in the lungs, re-enters the 

 heart at the left auricle, which is smaller than the right, but its 

 walls are thicker. It is situated at the left postero-superior part 



