876 



THE VASCULAR SYSTEM. 



part of the anterior boundary is the a trio- ventricular aperture or mitral orifice. 

 The orifice is oval in form ; its long axis is 'placed obliquely antero-posteriorly, and 

 from left to right, and is capable of admitting two fingers. It is guarded by a 

 valve formed of two large cusps, known as the mitral valve. 



Ventriculi. The ventricular portion of the heart is conical and somewhat 

 flattened. The base, directed upwards and posteriorly, is partly continuous with 

 the atrial portion and partly free. It is perforated by four orifices, the two 

 atrio-ventricular, the aortic, and the pulmonary. The atrio-ventricular orifices 

 are placed, one on each side, inferiorly and posteriorly ; anteriorly and between 



them is the aortic orifice, whilst the 

 orifice of the pulmonary artery is still 

 more anterior, and slightly to the 

 left of the aortic orifice. 



In the triangle between the atrio- 

 ventricular and the aortic orifices is 

 embedded a mass of dense fibrous 

 tissue which is the representative of 

 the os cordis of the ox. It is con- 

 tinuous with the upper part of the 

 interventricular septum, and with 

 fibrous rings which surround the 

 apertures at the bases of the ven- 

 tricles. 



The diaphragmatic surfaces and 

 the sterno-costal surfaces of the two 

 ventricles constitute respectively the 

 greater portions of the corresponding 

 surfaces of the heart ; the former 

 rest upon the diaphragm, whilst the 

 latter are directed upwards and 

 anteriorly towards the sternum and 

 the costal cartilages of the left side. 

 The apex of the left ventricle forms 

 the apex of the heart. 



The inferior margin of the ven- 

 tricular region, which is thin, forms 

 the inferior margin of the heart ; 

 and the left margin, which is thick 

 and rounded, forms the greater part 



FIG. 755. THE RELATIONS OF THE HEART AND THE 

 ATRIO - VENTRICULAR, AORTIC, AND PULMONARY 

 ORIFICES TO THE ANTERIOR THORACIC WALL. 



I to VII, Costal cartilages. 



A, Aortic orifice. 



Ao, Aorta. 



C, Clavicle. 



LA, Left atrium. 



LV, Left ventricle. 



M, Mitral orifice. 

 P, Pulmonary orifice. 

 HA, Right atrium, 

 RV, Right ventricle. 

 SVc, Superior vena cava. 

 T, Tricuspid orifice. 



the left margin of the heart. 



The ventricular portion of the heart is divided into right and left chambei 

 by the ventricular septum, which is placed obliquely, with one surface directed 

 anteriorly and to the right, and the other posteriorly and to the left ; it bul 

 into the right ventricle, and its lower margin lies to the right of the apex of 

 heart, which is, therefore, formed entirely by the left ventricle. The margins 

 the septum are indicated on the two surfaces of the ventricular part of the he 

 by anterior and inferior interventricular sulci. 



Ventriculus Dexter. The right ventricle is triangular in form. Its base 

 directed upwards and to the right, and, in the greater part of its extent, it 

 continuous with the right atrium, with which it communicates by the atric 

 ventricular orifice ; but its left and anterior angle is free from the atrium, am 

 gives origin to the pulmonary artery. Its inferior wall rests upon the diaphragi 

 The sterno-costal wall lies posterior to the lower part of the left half of tl 

 sternum and the cartilages of the fourth, fifth, and sixth ribs of the left sid< 

 The left or septal wall, which is directed posteriorly and to the left, bulges inl 

 its interior, and on this account the transverse section of the cavity has a semi 

 lunar outline. The cavity itself is a bent tube consisting of an inferior portion o? 

 body into which the atrio-ventricular orifice opens, and of an antero-superior 

 the infundibulum or conus arteriosus, which terminates in the pulmonary arter 



