THE RIGHT VENTRICLE. 



247 



orifices, protected by A^alves ; the aurtculo-ventriciilar, of an oval 

 form, and situate towards the right, and that of the j^n</7»o;2«r?/ 

 artery, smaller, more elevated, and towards the left. Between the two 

 the wall of the cavity projects downwards, in the form of a thick 

 rounded muscular partition. The inner surface is marked by muscular 

 bundles, " columnas carnea?," some of which are attached by each ex- 

 tremity to the wall of the ventricle and are free in the middle, others are 



Yv'. 169. 



Fig. 169. — Cross Section of the 

 Vektriculak pakt of the 

 Heart at two-thirds from 

 the Apex looking kownwards 

 INTO THE Cavities (Allen 

 Thomson). 2-3rd3 the 



natural size. 



1, 1', Wall of the riciht ventri- 

 cle ; 2, 2', wall of the left ; 3, 3', 

 septum ; 4, the principal papil- 

 lary muscle of the right ventricle ; 

 4', some columnfe carnere on the 

 septum near the front ; 4", others 

 posteriorly near the septum ; 5, 5', 

 the ijrincipal papillary muscles of 

 the left ventricle ; 6, the deepest 

 part of the cavity of the right 

 ventricle ; 7, that of the left ven- 

 tricle at the apex of the heart. 



only sculptured in relief, as it were, being- continuous with the wall of 

 the ventricle in their whole length ; while a third set, forming two prin- 

 cipal bundles, an anterior (fig. 167, 4',) and a posterior, named muscidi 

 ■papillarcs, are connected at their base with the ventricular wall, and by 

 the other end are attached to small tendinous cords {chordcc tendinece), 

 through which they are connected with the segments of the auriculo- 

 ventricular valve. The inside of the conus arteriosus is smooth, and 

 free from columnfe carnea?. 



The valve guarding the right auriculo-ventricular opening is com- 

 posed of three triangular segments, or flaps (anterior, right or inferior, 

 and posterior, or septal), and is hence named the friruspid. The flaps 

 are mainly formed of folds of the endocardium, enclosing fibrous tissue. 

 At their bases, they arc continuous with one another, so as to form an 

 annular membrane attached around the margin of the auricular open- 

 ing : they are directed downwards, and are retained in position within 

 the ventricle by the chordae tendinete, which are attached to their 

 ventricular surfaces and free margins. The middle part of each seg- 

 ment is thicker than the rest, whilst the marginal part is thin, trans- 

 parent, and jagged at the edges (compare fig. 173, B, e, e). 



The chords tendinete from the anterior papillary muscle pass to the cleft 

 between the anterior and inferior segments, to be attached to both : the chordte 

 tendineiE from the posterior papillary muscle are attached in like manner to the 

 posterior and inferior segments : while others fonning a third set sj^ring directly 

 from the surface of the septum, sometimes from small eminences upon it, and 

 pass upwards, to be attached to the adjacent borders of the anterior and poste- 

 rior segments. 



During the contraction of the ventricle, the segments of the valve are applied 

 to the opening leading from the amicle, and prevent the blood from rushing 

 back into that cavity. Being retained by the chorda3 tendinea;, the expanded 

 flaps of the valve resist the pressure of the blood, which would otherwise force 



