7i6 HUMAN ANATOMY. 



reflected upward over the anterior surface of the auricles until it again meets the 

 parietal layer. There is thus produced, between the aortae in front and the auricles 

 behind, a cavity or cleft, known as the transverse sinus of the pericardium (Fig. 654), 

 which is continuous at either extremity with the general pericardial cavity, and is 

 roofed in by the parietal layer, while its walls and floor are formed by the visceral 

 layer. 



In the roof of the sinus transversus a sHght fold is to be fourud towards the left, which 

 passes backward to the Hne of attachment of the roof to the left auricle and thence obliquely 

 downward in the \ isceral layer covering the posterior surface of the auricle towards the coro- 

 nary sinus. This duplicature, known as the vestigial fold oi the pericardium (ligamentum v. 

 cavae sinistrae), contains in its upper part a fibrous cord and in its lower part the oblique vein of 

 the left auricle ; these two structures, the vein and fibrous cord, together with the coronary 

 sinus, representing the remains of an original left superior vena cava. 



It may be noted that the line of attachment of the parietal layer between the left pul- 

 monary veins and the inferior vena cava extends high up on the posterior surface of the auricles, 

 and there is thus formed in this region a pouch-like diverticulum of the pericardium whose 

 mouth looks downward. This is what has been termed the oblique sinus of the pericardium. 

 Its parietal wall rests upon the oesophagus posteriorly, and in case of extensixe effusion into the 

 pericardial cavity, compression of the oesophagus sufficient to interfere with the act of swallow- 

 ing may result. 



The Ligaments of the Pericardium. — The parietal layer of the pericardium 

 is united to the surrounding structures by areolar tissue which may condense to definite 

 bands termed pericardial ligaments. Thus the tissue between the pericardium and 

 the sternum may condense to form a superior and an inferior periea7-dio-stemal liga- 

 ment, the former passing to the posterior surface of the manubrium sterni and the 

 latter to the lower part of the gladiolus. Similarly, bundles of fibres are attached to 

 the apex of the pericardial cone and to the great vessels of the heart, taking their 

 origin from the prevertebral layer of the cervical fascia which is prolonged downward 

 into the thorax ; these are \k\^ pericardia-vertebral ligaments. And, finally, a band 

 has been described as extending from the posterior surface of the pericardium to the 

 upper surface of the diaphragm on either side of the ^'ena cava inferior ; these form 

 what are termed \\\^ pcricardio-phrenic ligaments. 



The Vessels. — The arteries which supply the posterior surface of the parietal 

 layer of the pericardium arise from the thoracic aorta, and those of the anterior sur- 

 face are given ofi by the internal mammary artery. The veins of the parietal layer 

 pursue courses parallel with those of the arteries, and open into the vena azygos 

 behind and the superior phrenic or superior vena cava anteriorly. 



The lymphatics pass to the nodes lying in the bifurcation of the trachea. The vas- 

 cular supply of the visceral layer is the same as that of the muscular tissue of the heart. 



The nerves distributed to the pericardium include fibres from the phrenic nerve, 

 especially the left one, and also probably from the cardiac plexus. 



PRACTICAL CONSIDERATIONS : THE PERICARDIUM. 



The visceral layer of the pericardium is closely attached to and practically insep- 

 arable from the heart muscle. It is continuous with the parietal layer at the base of 

 the heart where the two layers ensheathe the great vessels, covering in especially 

 the first inch and a half of the aorta and pulmonary artery and leaving, between 

 those vessels in front and the auricles behind, an open space — the transverse sinus — 

 which may be the seat of an effusion walled off by adhesions from the general peri- 

 cardial cavity. The least resistant important structure in immediate relation to this 

 sinus is the superior vena cava, — also intrapericardial at its lowermost portion, — and 

 such effusion might therefore cause fulness of the veins of the neck or even cyanosis 

 without the evidence of a general pericardial dropsy large enough to give the usual 

 concomitant physical signs {vide infra). In artificial distention of the pericardium 

 the sac tends to assume the shape of two irregular spheres, the upper or smaller one 

 containing the great vessels just mentioned, the lower embracing the heart, the 

 ascending cava, and the pulmonary veins. At the ape.x of the heart, where the peri- 

 cardium is reflected from the diaphragm, unimportant sinuses, analogous to the 

 costo-phrenic sinus of the pleura, may exist. 



