RIGHT VENTEICLE. 391 



EIGHT VENTRICLE. 



The blood leaves the right auricle through the auriculo-ven- 

 tricular opening, and enters the right ventricle, which occupies 

 the antero-inferior part of the right side of the heart. It is some- 

 what conical in shape, with its base uppermost, and extends from 

 the auriculo-ventricular septum to near the apex. Its outer walls, 

 although thicker than those of the auricle, are much thinner than 

 those of the left ventricle. The inner wall is convex, and formed 

 by the interventricular septum ; on laying the cavity open (by 

 an incision along the side of the anterior longitudinal furrow, and 

 a second one below and parallel to the transverse septum, joining 

 the first), two openings present themselves. 



The auriculo-ventricular is the large oval opening, situated at 

 the base of the ventricle, surrounded by the fibrous auriculo-ven- 

 tricular ring; it communicates with the auricle, and is guarded 

 by the tricuspid valve, which is formed by a redoublicature of 

 the endocardium, strengthened by an intermediate layer of fibrous 

 tissue. It consists of three triangular cusps or segments, which, 

 connected at their bases, surround the auricular opening. The 

 cusps are attached to each other above for a short distance, but 

 their apices freely project into the cavity of the ventricle ; the 

 largest is placed between the auriculo-ventricular opening and the 

 opening of the pulmonary artery ; a second rests against the 

 septum of the ventricles, the third between the other two. The 

 free edges of the cusps are thickened, and to their ventricular 

 surfaces and free margins are attached a number of delicate 

 tendinous cords, or chordce tendinece, which spring from the inner 

 surface of the ventricle. The majority of these arise from the 

 free blunt extremities of the muscuU papillares, which are a 

 variety of carnece columnce, the remainder from the walls of the 

 ventricle, diverging towards the valve ; some terminate in the 

 free margins and apices of the cusps, others in the central thick 

 portion ; while a few reach the attached borders, and become 

 continuous with the auriculo-ventricular ring. This valve pre- 

 vents the regurgitation of blood into the auricle when the ventricle 

 contracts. 



The second opening in the right ventricle is the origin of the 

 pulmonary artery. It is situated above and to the left of the 

 auriculo-ventricular opening, is circular, and arises from the 

 summit of a conical prolongation called the conus arteriosus, or 



