The Heart. 



373 



Valvula semilunaris anterior a. pulmonalis ' 



I Conns arteriosus 



Valvula semilunaris 

 sinistra a. pulmonali 



Valvula semi- / 



lunaris sinistra /_ 



aortae / 



I 



Trigona fibrosa ^ -/ 



N'alvula semilunaris 

 '^ dextra a. pulmonalis 



Valvula semilunaris 

 dextra aortae 



Valvula semilunaris 

 posterior aortae 



Cuspis ante- 



rior valvulae__/. 



bicuspidalis / 



[mitralisj / 



Cuspis poste- I 



rior valvulaej 



bicuspidalis r 



fmitralisl ' 



valvulae 

 tricus- 

 pidalis 



Cuspis 

 anterior 



_ Cuspis 

 > medialis 



Cuspis 

 posterior 



1 Annulus fibrosus 



' dexter 



Annulus flbrosus sinister 



>Ventriculus dexter 



419. Base of the contracted ventricles, 



after removal of the fore -chambers or atria. The valves are closed. 



(The outlines of the distended ventricles are indicated in red, the position of the ostium 



arteriosmn sinistruni being assumed to he fixed.) 



The anuiili flbrosi are dense, narrow bands of connective tissue, which surround the 

 ostia venosa at the base of the ventricles. They serve for the attachment of the nniscular fibers 

 of the atria and of the ventricles, and from them arise in largest part the valvulae tricuspidalis 

 and bicuspidalis. The right surrounds the ostium venosum dextrum in the form of an oval 

 closed ring. The left is horseshoe- shaped surrounding the right, posterior and left sides 

 of the ostium venosum smistnuu; it begins right and left at the root of the aorta in a nodular 

 thickening on either side, the trigona fibrosa ; between these the anterior cusp of the valvula 

 bicuspidalis arises directly from the membranous wall- of the root of the aorta. 



The differences between the contracted and dilated ventricles are as follows 

 (see also Figs. 413. 414, 417 and 41 S): 



In the dilated ventricles the diameter of the base is nearly the same as that of the 

 long axis; the form approaches that of a hemisphere. The conus arteriosus projects markedly, 

 the lower surface bulging much less than the upper, the ostia venosa and arteriosa are large, 

 the cavities of the ventricles are wide open; the trabeculae cameae extend partly tbrough the 

 lumen of the ventricles, and the musculi papillares stand out partly free in the ventricular cavities. 



On maximal contraction of the ventricles, the diameter of the base is markedly shortened, 

 while that of the long axis diminishes only slightly; the form is wedge-shaped. The conus 

 arteriosus shortens and sinks in: the facies diaphragmatica is slightly flattened, the s\ilcus 

 longitudinalis anterior has a more marked spiral twist, the ostia venosa are markedly diminished 

 in size, the ostia arteriosa less markedly, the cavities of the ventricles are represented only by 

 a slit (with the exception of a s]>aee situated above the apices of the papillary muscles); the 

 trabeculae cameae and the musculi papillares lie close to the walls and form ridge-like projections. 



