532 ANGIOLOGY 



by intervening layers of fibrous tissue: their central parts are thick and strong, 

 their marginal portions thin and translucent, and in the angles between the latter 

 small intermediate segments are sometimes seen. Their bases are attached to a 

 fibrous ring surrounding the atrio ventricular orifice and are also joined to each other 

 so as to form a continuous annular membrane, while their apices project into the 

 ventricular cavity. Their atrial surfaces, directed toward the blood current from 

 the atrium, are smooth; their ventricular surfaces, directed toward the wall of the 

 ventricle, are rough and irregular, and, together with the apices and margins of 

 the cusps, give attachment to a number of delicate tendinous cords, the chordae 

 tendinese. 



Right auricula. 



Right 

 atrium 



Left 

 auricula // ' Eight pulmonary 



V veins 



Left pulmonary veins 



FIG. 494. Heart seen from above. Fio. 495. Base of ventricles exposed by removal 



of the atria. 



The trabeculse carnese (columnoe carnece) are rounded or irregular muscular 

 columns which project from the whole of the inner surface. of the ventricle, with 

 the exception of the conus arteriosus. They are of three kinds: some are attached 

 along their entire length on one side and merely form prominent ridges, others 

 are fixed at their extremities but free in the middle, while a third set (musculi 

 papillares) are continuous by their bases with the wall of the ventricle, while their 

 apices give origin to the chordae tendinese which pass to be attached to the seg- 

 ments of the tricuspid valve. There are two papillary muscles, anterior and pos- 

 terior: of these, the anterior is the larger, and its chordae tendineae are connected 

 with the anterior and posterior cusps of the valve : the posterior papillary muscle 

 sometimes consists of two or three parts; its chordae tendineae are connected 

 with the posterior and medial cusps. In addition to these, some chordae tendineae 

 spring directly from the ventricular septum, or from small papillary eminences on it, 

 and pass to the anterior and medial cusps. A muscular band, well-marked in sheep 

 and some other animals, frequently extends from the base of the anterior papillary 

 muscle to the ventricular septum. From its attachments it may assist in preventing 

 overdistension of the ventricle, and so has been named the moderator band. 



The pulmonary semilunar valves (Fig. 494) are three in number, two in front 

 and one behind, formed by duplicatures of the lining membrane, strengthened 

 by fibrous tissue. They are attached, by their convex margins, to the wall of the 

 artery, at its junction with the ventricle, their free borders being directed upward 

 into the lumen of the vessel. The free and attached margins of each are strength- 



