554 THE VASCULAR SYSTEMS 



of which to the parietal layer presents the shape of an inverted O. The cul-de-sac enclosed 

 between the limbs of the O is known as the oblique sinus, while the passage between the venous 

 and arterial mesocardia i. e., between the aorta and pulmonary artery in front and the auricles 

 behind is termed the transverse sinus (sinus transversus pericardii). The serous pericardium 

 is smooth and glistening, and transudes a serous fluid, which serves to facilitate the movements of 

 the heart. 



The Vestigial Fold of the Pericardium. Between the left pulmonary artery and subjacent 

 pulmonary vein and behind the left extremity of the transverse sinus is a triangular fold of the 

 serous pericardium; it is known as the vestigial fold of Marshall (licjamentum v. cavaesinistrae). 

 It is formed by the duplicature of the serous layer over the remnant of the lower part of the 

 fetal left superior vena cava (v. cava sinistra), or the duct of Cuvier, which becomes impervious 

 after birth, and remains as a fibrous band stretching from the left superior intercostal vein 

 to the left auricle, where it is continuous with a small vein, the oblique vein of Marshall 

 (v. obliqua atrii sinistri [Marshalli]), which opens into the coronary sinus. 



The arteries of the pericardium are derived from the internal mammary and its musculo- 

 phrenic branch, and from the descending thoracic aorta. 



The nerves of the pericardium are derived from the vagi, the phrenics, and the sympathetics. 



Applied Anatomy. The effusion of fluid into the pericardial sac often occurs in acute rheu- 

 matism or pneumonia, or in patients with chronic vascular and renal disease, embarrassing 

 the heart's action and giving rise to signs of cardiac distress, such as pallor, a rapid and feeble 

 pulse, dyspnea, and restlessness. On examination, the apical cardiac impulse is absent, or 

 replaced by a more extensive indefinite and wavering pulsation; it may appear to be in the 

 second, third, or fourth left space, and is then not an apex impulse, as Potain has stated, but 

 due to the impact of some portion of the heart wall nearer its base. In children the precordial 

 intercostal spaces may bulge outward. The most striking sign, however, is the great increase 

 in all directions of the precordial dulness on percussion. This becomes pear-shaped, the stalk 

 of the pear reaching up to about the left sternoclavicular articulation; the dulness also extends 

 some distance to the right of the sternum, particularly in the fifth interspace (Rotch). The 

 fluid collects mainly on either side of the heart, and below it, especially on the left side, where 

 the Diaphragm can yield more readily to pressure than it can on the right. Ewart has drawn 

 attention to the presence of a square patch of dulness over the base of the left lung behind, 

 reaching up to the level of the ninth or tenth rib, and extending outward as far as the lower 

 angle of the scapula; the underlying lung tissue gives the physical signs of compression or 

 collapse. 



Paracentesis of the pericardium is often required to relieve the urgent cardiac or respiratory 

 distress in these cases, and should be performed without hesitation and before the patient is in 

 extremis. It may also be required when the pericardium is filled with blood or pus, and as it 

 is advisable to perform this operation without transfixing the pleura, the puncture should be 

 made either in the fifth or sixth intercostal space on the left side and close to the sternum, so 

 as to avoid wounding the internal mammary artery, which descends about half an inch from 

 the sternal margin; or the needle may be entered at the left costoensiform angle and made to 

 pass upward and backward behind the lower end of the body of the sternum into the pericardial 

 sac. It must be remembered that even in the largest pericardial effusions, the heart itself lies 

 almost in contact with the anterior wall of the thorax, and great care must be exercised to avoid 

 piercing this organ. 



Pericardiotomy is required when the effusion is of a purulent nature. In this operation a 

 portion of the fifth or sixth costal cartilage is excised. An incision is made along the left 

 border of the sternum from the upper border of the fourth cartilage to the seventh. Trans- 

 verse incisions an inch long are then made outward from either extremity of this, and the rect- 

 angular flap thus formed reflected outward. The fifth costal cartilage is now separated from 

 the sternum by means of a gouge, great care being taken not to let the instrument slip and pene- 

 trate too deeply. The cartilage is then seized with lion forceps and raised, the tissues beneath 

 it being peeled off, so as to avoid wounding the internal mammary artery or the pleura. The 

 Triangularis sterni is now scratched through with a director or the nail of the index finger close 

 to the sternum, and the pericardium felt for and opened, the finger guarding the pleura and 

 left internal mammary artery. 



THE HEART (COR). 



The heart is a hollow muscular organ of a conical form, placed between the 

 lungs, and enclosed in the cavity of the pericardium. 



Position (Fig. 414). The heart is placed obliquely in the thorax behind the 

 gladiolus and adjoining parts of the rib cartilages, and projects farther into the 



