464 



DISSECTION OF THE THOKAX. 



Position of 

 apertures 



of arteries, 



pulmonary, 

 aortic ; 



sounds 

 heard best 



auriculo- 

 ventricular 

 openings : 

 left; 



right. 



Vessels 



joining the 

 heart. 



The pulmo- 

 nary artery 



divides into 

 two for the 

 lungs. 



Right 

 branch. 



While the blood is entering the cavity, the cusps of the valve are 

 separated ; and when the ventricle contracts, they meet to close the 

 passage into the left auricle. In combination with the tricuspid it 

 assists in producing the first sound of the heart. The examination 

 of the aortic opening will be deferred until the large vessels at the 

 base of the heart have been studied ; it is described on page 473. 



SURFACE MARKING OF THE VALVULAR APERTURES. Two openings 

 have been seen in each ventricle, one of the auricle of its own side, 

 of the heart, and one of an artery. 



The apertures of the arteries (aorta and pulmonary) are neaivsi 

 the interventricular septum ; and as the two vessels were originally 

 formed from one tube, they are close together ; but of the two, the 

 pulmonary artery is anterior and more to the left, as well as some- 

 what higher. As regards the surface the pulmonary valve is behind 

 the junction of the third left costal cartilage with the sternum near 

 the upper border of the cartilage and the aortic is just under cover 

 of the sternum opposite the lower part of the same cartilage. 



The sound produced at the pulmonary orifice is heard best in the 

 second left intercostal space, and that produced at the aortic orifice 

 in the second right intercostal space. 



The auriculo-ventricular openings are nearer the circumference 

 of the heart, and each is posterior to the artery issuing from the fore 

 part of its ventricle. The left auriculo-ventricular opening is 

 nearest of all to the back of the heart, and is marked on the surface 

 by a line extending inwards and a little downwards to the middle 

 of the sternum from the upper part of the fourth left costal cartilage 

 at its junction with the sternum. 



The right auriculo-ventricular opening is situated behind the 

 right half of the sternum opposite the fourth intercostal space in a 

 line passing downwards and a little to the right. 



Dissection. The large vessels between the base of the heart 

 and the upper opening of the thorax w r ill now be made ready 

 for examination and the parts upon which they lie carefully 

 cleaned. 



GREAT VESSELS. The arteries which take origin from the heart 

 are the aorta and the pulmonary trunk. The large veins entering 

 the heart, besides the coronary sinus, are the superior and inferior 

 cavse, and the pulmonary. 



The PULMONARY ARTERY (fig. 163, p. 448, and fig. 164, p. 452), 

 is a short thick trunk, which conveys the dark blood from the right 

 side of the heart to the lungs. From its commencement in the 

 right ventricle the vessel is directed upwards and backwards on the 

 left of the aorta ; and at a distance of an inch and a half or two 

 inches, it divides into two branches for the lungs. The trunk of 

 the pulmonary artery is contained in the pericardium ; and beneath 

 its lower end is the beginning of the aorta. On each side are the 

 coronary artery and the auricular appendix. 



The right branch is longer and somewhat larger than the left. 

 In its course to the lung it passes outwards above the right auricle 

 of the heart, and behind the aorta and superior vena cava. 



