18 EXERCISE IV 



turn back the sternum with its cartilages attached, bending or breaking it at the 

 4th space, and retracting it (PI. I, fig. 3) when so reversed with a heavy hook- 

 weight. 



V. Note (1) the rhythmically inflated lung lobes (PI. I, fig. 8 (l)) of pale 

 pink colour, (2) the heart beating in the pericardial sac (PI. I, fig. 3 (s)) ; also 

 (3) the thymus and the diaphragm, and the superior vena cava (PI. I, fig. 3 (v)). 

 Regulate the lung inflation to reduce conveniently the lung expansion so that it 

 does not obscure the view of the heart. Note that the lungs, even when 

 inflated fully, do not cover wholly the front of the heart and pericardium. 

 This area not covered by the lungs is delimitable on the front of the unopened 

 chest by percussion, and is known as the ' area of precordial dullness '. Note 

 the right phrenic nerve coursing along the right side of the pericardium to 

 reach the diaphragm. 



Obs. 11. VI. With fine forceps pick up a small fold of the pericardium not far 



intr °* °^ ^*^^^^s from the apex of the heart ; cut with fine scissors an opening about 4 mm. 

 dial pressure, long in the pericardial sac. Insert through this opening the nozzle of the 

 pericardial cannula (PI. I, fig. 4) and tie it securely in by a ligature embracing 

 the hole in a water-tight way. Connect the cannula with the rubber tube 

 from the saline manometer. The saline should be warm, about 35° C. 

 Starting with zero-pressure in the pericardium, gradually raise with the hand 

 the funnel attached sidewise to the manometer system and so increase the 

 pressure in the percardial sac. Observe the increments on the manometer 

 scale, and the effect upon the heart. The pericardium is sufficiently 

 transparent to allow the auricles to be watched ; observe especially the right 

 auricle. The pressure should not be increased beyond 6 cm. of water. Note 

 impending asphyxia, and the onset of asphyxial convulsions. Do not carry 

 the experiment at all beyond that point ; when it is reached, at once relieve 

 the intrapericardial pressure by freely opening the pericardial sac ; scissors 

 should be ready at hand for doing this without delay. Remove the cannula 

 and pericardial injection apparatus. 



Obs. 12. VII. Bare the heart freely from the pericardium (PI. I, fig. 5). Note 



Further inspec- the movements of systole and diastole, and the twisting motion of the heart 



^°e^t vessell*^^ accompanying them. Note the colours of right and left auricles respectively. 



in situ. Make out clearly the aorta, pulmonary artery, and superior and inferior 



venae cavae. Note the difference in colour between sup. vena cava and 



the pulmonary veins. Note the ' sinuses of Valsalva ', especially well seen at 



the root of the pulmonary artery. Turn the heart towards the preparation's 



