THE HEART 1369 



The valves. — The pulmonary valves (the highest and most superficial) lie, in 

 front of the aortic, behind the third left chondro-sternal joint, and opposite to 

 the upper border of the third costal cartilage. The aortic valves lie behind and a 

 little below these, opposite to the medial end of the third intercostal space, 

 and on a level with the lower border of the third left costal cartilage. The 

 atrio -ventricular openings lie at a somewhat lower level than that of the aortic 

 and pulmonary. Thus the tricuspid valves lie behind the middle of the sternum 

 at the level of the fourth intercostal space; and the mitral valves, the most deeply 

 placed of all, lie a little to the left of these, behind the left edge of the sternum 

 and the fourth left costal cartilage (fig. 1107; also cf. fig. 437). 



'Thus these valves are so situated that the mouth of an ordinary-sized stethoscope will 

 cover a portion of them all, if placed over the juncture of the third intercostal space, on the left 

 side, with the sternum. All are covered by a thin layer of lung; therefore we hear their action 

 better when the breathing is for a moment suspended.' (Holden.) 



The pericardium. — This fibro-serous sac, occupying the middle mediastinum, 

 is triangular in shape, with the apex upward. Here its fibrous laj-er gives invest- 

 ment to the large vessels, except the inferior cava. It is also continuous with the 

 deep cervical fascia. The base, connected with the diaphragm, has been referred 

 to above. In front an area of variable size (fig. 1107), owing to the divergence 

 of the left pleura, is in contact wdth the left half of the lower part of the sternum, 

 and more or less of the medial ends of the fourth, fifth, and sixth costal cartilages, 

 here forming the posterior boundary of the anterior mediastinum. Behind, the 

 pericardium is the anterior boundary of the posterior mediastinum, and is in 

 close contact with the oesophagus and aorta. 



Paracentesis of pericardium. — While the seat of election must here remain an open question, 

 each case requiring a decision for itself, the one most suitable on the whole is the fifth left space, 

 about 2.5 cm. (1 in.) from the sternum, so as to avoid injury to the internal mammary artery 

 and the pleura, of which the line of reflection has been shown to vary. 



In incision of the pericardium to establish free drainage, a portion of the fifth or sixth left 

 costal cartilage should be carefully resected, the internal mammary artery tied, the trans- 

 versus thoracis (triangularis sterni) scratched through, and the pleural reflexion pushed aside. 



Relation of vessels to the wall of the thorax. — Aortic arch. — The ascending part of the 

 aorta reaches from a spot behind the sternum, a little to the left of the centre, on a level with the 

 third left costal cartilage, to the upper border of the second right cartilage; thus it passes up- 

 ward, backward, and to the right, and is about 5 cm. (2 in.) long. The transverse part then 

 crosses backward to the left behind the sternum (the highest part of the arch being about 2.5 

 cm. (1 in.) below the notch), reaching from the second right costal cartilage to the lower border 

 of the fourth thoracic vertebra on the left side. This part recedes from the surface, and, with 

 the next, cannot be marked out on the surface. The third, or descending part, the shortest 

 of the three, reaches from the lower border of the fourth to that of the fifth thoracic vertebra. 



Fig. 1104 will remind the reader of many of the pressure symptoms which maj' accompany 

 an aneurysm of the aortic arch; e. g., pressure on the left innominate vein, the three large arte- 

 ries, trachea, and left bronchus, recurrent nerve, oesophagus, and thoracic duct. In aneurysm 

 of the thoracic aorta, pain, usually unilateral, referred to the corresponding intercostal nerves, 

 is a common pressure symptom. 



The pulmonary artery lies behind the left side of the sternum and its junction with the sec- 

 ond and third costal cartilages. 



Innominate artery. — A line drawn from the top of the arch, about 2.5 cm. (1 in.) below 

 the sternal notch, and close to the centre, to the right sterno-clavicular joint, will give the line 

 of this vessel. 



Left common carotid. — This vessel will be denoted by a line somewhat similar to the above, 

 passing from the level of the arch a little to the left of the last starting-point to the left sterno- 

 clavicular joint. 



Left subclavian artery. — A line from the end of the transverse arch, behind the left of the 

 sternum, straight upward to the clavicle, delineates the vertical thoracic course of the long left 

 subclavian artery; its thoracic portion lies behind the left carotid. 



Innominate veins. — The left, 7.5 cm. (3 in.) long, extends very obliquely from the left 

 sterno-clavicular joint, behind the upper part of the manubrium, to a point 1.2 cm. (i in.) to 

 the right of the sternum, on the lower border of the first right costal cartilage. The right, 

 about 2.5 cm. (1 in.) long, descends almost vertically to the above point from the right sterno- 

 clavicular joint. 



Venae cavae. — The superior descends from the point above given for the meeting of the 

 innominate veins in the first intercostal space, close to the sternum, and perforates the right 

 atrium on a level with the third costal cartilage. The inferior vena cava, — The opening of this 

 vein into the right atrium lies under the middle of the fifth right interspace and the adjacent 

 part of the sternum. 



The oesophagus. — The relations of this tube in its cervical and thoracic 

 portions are most important, e.g., to the trachea and left bronchus; the vagi 

 and left recurrent nerve; the pleurae, left above and right ibelow, aorta, and 



