352 



THE HEART. 



by a membranous covering, the pericardium. These structures, covered on each side 

 by the parietal pleura, constitute the chief part of the middle mediastinum, the 

 largest division of the median thoracic septum which, extending from spine to 

 sternum, separates the two pleural cavities. The heart lies nearer to the front than 

 the back of the chest, but is for the most part separated from the anterior thoracic 

 wall by the pleurae and the thin anterior portions of the lungs. 



THE PERICARDIUM. 



This membranous sac, in which the heart is contained, is of a somewhat conical 

 shape, its base resting on the diaphragm, while the upper narrower part surrounds 

 the trunks of the great vessels. It consists of two layers, one external and fibrous, 

 the other internal and serous. 



The fibrous layer is a dense, unyielding membrane, consisting of fibres which 

 interlace in every direction. This layer is attached below to the upper surface of 



Fig. 305. SEMIDIAGRAMMATIC 



VIEW OP THE PERICARDIUM 

 FROM BEHIND, DESIGNED TO 

 SHOW THE PRINCIPAL INFLEC- 

 TIONS OF THE SEROUS SAC 

 ROUND THE GREAT VESSELS. 



(Allen Thomson.) 



The drawing is taken from 

 preparations in which the heart 

 and vessels had been partially 

 filled by injection, the pericar- 

 dium inflated and dried in the 

 distended state, and the fibrous 

 continuation on the vessels re- 

 moved. By the removal of a por- 

 tion of the pericardium from be- 

 hind the right and left cavities 

 of the heart, the position of that 

 organ is made apparent. A, right 

 auricle ; A', left auricle ; V, right 

 ventricle ; V', left ventricle ; Ao, 

 aortic arch ; b, innominate artery ; 

 0, vena cava superior ; az, azygos 

 vein ; C", vena cava inferior ; c", 

 great coronary vein ; + , liga- 

 mentum arteriosum ; P, right, P, 

 left pulmonary artery ; p, right, 

 p', left pulmonary veins ; Z), cen- 

 tral tendon of diaphragm ; 1, sac 

 of pericardium ; 2, the portion 

 on the right side which partially 

 surrounds the superior vena cava, 

 the right pulmonary veins, and 

 the inferior vena cava ; 3, portion 



on the left side which partially surrounds the inferior vena cava ; 4, portion which is extended upwards 

 behind the left auricle, and partially folds over the pulmonary arteries and veins, meeting between 

 these different vessels the extensions of the sac from the right and left ; 5, upper part of the transverse 

 sinus passing behind the aortic and pulmonary arterial trunks. A bent probe is passed within the 

 pericardium from behind the right auricle, in front of the inferior vena cava, to the back of the left 

 ventricle, which may indicate the place where the large undivided sac of the pericardium is folded round 

 that vein. 



the diaphragm (fig. 305, D), partly to the central tendon, partly to the adjoining 

 muscular surface, especially on the left side. Near the median line the connection 

 is very firm, the fibrous structures being continuous ; elsewhere the attachment is 

 more lax, and is effected mainly by areolar tissue. The pericardium is supported also 

 in front by two variable fibrous bands, the superior and inferior sterno-pericardial 

 ligaments of Luschka, which pass to it from the manubrium and ensiform process of 



