THE HEART 



981 



ovalis. Bcneatli its upper inaririn a little valvular i)OU{li may usually l»e notiet'd 

 Avhicli leads iuto a small orifice ])assin,i^ iuto the left auricle. 



The tubercle of Lower — which is jtlaced on the rijiht of the cavity between the 

 orifices of the two cavte — is well marked in some of the lower animals, hut it is quite 

 an insignificant eminence in man. 



The right ventricle forms the larger })art of the heart in front, where it is 

 convex; hut helow, where it rests upon the diaphragm, it is flattened. It forms 

 the whole of the lower l)order (iiiargo acuti(s) of the heart, but it does not reach the 

 apex, which is formed entirely by the left ventricle. 



It lies l)ehind the lower part of the body of the sternum and the cartilages of 

 the fifth, sixth, and seventh ribs of the left side. 



In form the ventricle is triangular, in section semilunar, and its walls are much 

 thinner than those of the left ventricle. Its upper and left angle is continuous 

 Avith the root of the pulmonar}' artery; and ujjon opening the cavity the two are 

 seen to be continuous through a cone-shaped prolongation — the infundibulum or 

 conus arteriosus. 



At the opposite angle there is a second and larger opening, leading from the 

 right auricle, the auriculo-ventricular orifice. It lies below and to the right of the 

 jiulmonary orifice. The apex of the ventricle points to the left. 



Fig. 5.50. — Traxsversp: Sectiox through the Heart xear its Apex. Showixg the Rela- 

 tive Thickness of its Muscular Walls, the Bulging of the Sf.ptum towards the 

 Kight Ventricle, and the Shape of the Cavities. 



CAVITY OF LEFT 

 VENTRICLE 



CAVITY OF RIGHT 

 VENTRICLE 



Section of papil- 

 lary muscle 



Posterior coronnri/ 



arti-ni 



Th(^ two openings just named are guarded by valves and se])arated by a rounded 

 muscular projection of the ventricular wall. The inner surface, or body, of the 

 ventricle ])resents a somewhat complicated arrangement of muscular ridges, bands, 

 and columns, which become smaller, more numerous, and more closely interlaced 

 at the a})ex and near the margin, but which disappear in the infundibulum. 



These projections, or columnae carneae, are usually divided into three sets : 

 (1) mere ridges: (2) bands attached to either end but elscAvhere free; and (8) a third 

 set, the musculi papillares, which need a more detailed description (fig. 549). 



A special band, the so-called moderator band, which is constant in the .sheei>, 

 is occasionally a well-marked structure in tlie luniian heart, stretching between its 

 anterior and sej)tal walls. The musculi papillares are attached l>y their broad 

 end to the ventricular Avail, and liy their extreiiiiiies to tendinous cords (chordae 

 tendineae), Avhich restrain and harmonise the action of the valves guarding the 

 auiicul(j-ventricular oi)ening. Three of these are larger and more constant than 

 the rest: an anterior, connected Avith the front Avail aboA-e the moderator band; a 

 right, near the margin, Avhich is also attached to the anterior Avail; and a posterior, 

 Avhich arises from the septum. The septal Avail of the A-entricle so bulges into the 

 cavity as to make its cross-section appear crescentic. 



