760 THE THORAX. 



The Right Ventricle is triangular in form, and extends from the right- auricle 

 to near the apex of the heart. Its anterior or upper surface is rounded and 

 convex, and forms the larger part of the front of the heart. Its posterior or 

 under surface is flattened, rests upon the Diaphragm, and forms only a small 

 part of the back of the heart. Its inner wall is formed by the partition be- 

 tween the two ventricles, the septum ventricnlorum, the surface of which is 

 convex, and bulges into the cavity of the right ventricle. Superiorly, the ven- 

 tricle forms a conical prolongation, the infundibulum, or conus arteriosus, from 

 which the pulmonary artery arises. The walls of the right ventricle are thinner 

 than those of the left, the proportion between them being as 1 to 2 (Bizot). 

 The wall is thickest at the base, and gradually becomes thinner towards the 

 apex. The cavity, which equals that of the left ventricle, is capable of -con- 

 taining about two fluidounces. 



To examine the interior, an incision should be made a little to the right of the anterior ven- 

 tricular groove from the pulmonary artery to the apex of the heart, and should be carried up 

 from thence along the right border of the ventricle, as far as the auriculo-ventricular opening. 



The following parts present themselves for examination : 



Openings \ Auriculo-ventricular. 



( Opening or the pulmonary artery. 



Valves . . T^M 



( Semilunar. 



And a muscular and tendinous apparatus connected with the tricuspid valve : 

 Columnar earner. Chords tendineas. 



The auriculo-ventricular orifice is the large oval aperture of communication 

 between the auricle and ventricle. It is situated at the base of the ventricle, 

 near the right border of the heart, and corresponds to the centre of the sternum 

 between the third costal cartilages. The opening is about an inch in diameter, 1 

 oval from side to side, surrounded by a fibrous ring, covered by the lining mem- 

 brane of the heart, and rather larger than the corresponding aperture on the 

 left side, being sufficiently large to admit the ends of three fingers. It is 

 guarded by the tricuspid valve. 



The opening of the pulmonary artery is circular in form, and situated at the 

 summit of the conus arteriosus, close to the septum ventriculorum. It is placed 

 on the left side of the auriculo-ventricular opening, upon the anterior aspect of 

 the heart, and corresponds to the upper border of the third costal cartilage of 

 the left side, close to the sternum. Its orifice is guarded by the pulmonary 

 semilunar valves. 



The tricuspid valve consists of three segments of a triangular or trapezoidal 

 shape, formed by a duplicature of the lining membrane of the heart, strength- 

 ened by a layer of fibrous tissue, and containing, according to Kurschner and 

 Senac, muscular fibres. These segments are connected by their bases to the 

 auriculo-ventricular orifice, and by their sides with one another, so as to form 

 a continuous annular membrane, which is attached round the margin of the 

 auriculo-ventricular opening, their free margins and ventricular surfaces afford- 

 ing attachment to a number of delicate tendinous cords, the chordse tend, 

 The largest and most movable segment is placed towards the left side of the 

 auriculo-ventricular opening ; interposed between that opening and the pulmo- 



1 In the Pathological Transact inns, vol. vi. p. 119, Dr. Peacock has given some careful re- 

 searches upon the weight and dimensions of the heart in health and disease. He states as the 

 result of his investigations, that, in the healthy adult heart, the right auriculo-ventricular aper- 

 ture has a mean circumference ( >f ,Y1.1 lines, or-l!'| inches; the left aiiriculo-ventrieiilar aperture 

 a mean circumference of 1 \.:\ lines, ;{; inches ; the pulnionic orifice of 40 lines, or 3' inches; 

 and the aortic orifice of .'!.">.;"> lines, or ;{,;', inches; but the dimensions of the orifice varied 

 greatly in different cases, the right auriciilo-vcntrk-ulai 1 aperture having a range of from 4.") to GO 

 lines, and the others in the same proportion. 





