THE HEART 



535 



The aortic semilunar valves (Figs. 494, 497) are three in number, and surround 

 the orifice of the aorta; two are anterior (right and left) and one posterior. They 

 are similar in structure, and in their mode of attachment, to the pulmonary semi- 

 lunar valves, but are larger, thicker, and stronger; the lunulse are more distinct, 

 and the noduli or corpora Arantii thicker and more prominent. Opposite the valves 

 the aorta presents slight dilatations, the aortic sinuses (sinuses of Valsalva), which 

 are larger than those at the origin of the pulmonary artery. 



The trabeculae carneae are of three kinds, like those upon the right side, but 

 they are more numerous, and present a dense interlacement, especially at the 

 apex, and upon the posterior wall of the ventricle. The musculi papillares are two 

 in number, one being connected to the anterior, the other to the posterior wall; 

 they are of large size, and end in rounded extremities from which the chordae 

 tendinese arise. The chordse tendinese from each papillary muscle are connected 

 o both cusps of the bicuspid valve. 



Left auricula 



Inferior 

 vena cava 



Membranous 

 septum 

 Musculi 

 pectinati 



Aortic valve 



Pipillary 

 muscles 



Anterior papillary muscle 

 FIG. 498. Section of the heart showing the ventricular septum. 



Ventricular Septum (septum ventriculorum; interventricular septum) (Fig. 498). 

 The ventricular septum is directed obliquely backward and to the right, and is 

 curved w r ith the convexity toward the right ventricle: its margins correspond 

 with the anterior and posterior longitudinal sulci. The greater portion of it is 

 thick and muscular and constitutes the muscular ventricular septum, but its upper 

 and posterior part, which separates the aortic vestibule from the lower part of 

 the right atrium and upper part of the right ventricle, is thin and fibrous, and is 

 termed the membranous ventricular septum. An abnormal communication may 

 exist between the ventricles at this part owing to defective development of the 

 membranous septum. 



Structure. The heart consists of muscular fibers, and of fibrous rings which serve for their 

 attachment. It is covered by the visceral layer of the serous pericardium (epicardium) , and 

 lined by the endocardium. Between these two membranes is the muscular wall or myocardium. 



The endocardium is a thin, smooth membrane which lines and gives the glistening appear- 





