THORACIC CAVITY 45 



From the upper end of the posterior longitudinal incision on 

 the left side an oblique cut must be made downwards and 

 backwards, along the line of the anterior surface of the root of 

 the left lung. When the incisions have been made, the anterior 

 flaps can be turned forwards and the posterior flaps downwards. 

 None of the flaps must be removed, for it will be necessary to 

 replace them in position at a later stage of the dissection. 



When the flaps marked out by these incisions are turned 

 aside, the dissectors will find that, on the right side, they have 

 exposed the greater part of the right atrium (see Fig. 13). They 

 should note that the area of the atrium which is exposed is 

 separated into two parts by a vertical sulcus, the sulcus terminalis, 

 which runs from the anterior face of the cardiac end of the 

 superior vena cava to the anterior aspect of the terminal part of 

 the inferior vena cava. This sulcus divides the atrium into a 

 posterior part, the sinus venarum, and an anterior part, the 

 atrium proper. The upper and anterior part of the atrium is 

 prolonged medially to the anterior surface of the heart. On the 

 left side," the greater part of the heart exposed by the reflection 

 of the pericardial flaps is the left ventricle, but in the upper part 

 of the area the auricle (O.T. auricular appendage) of the left 

 atrium is seen. Anterior to it lie the stem of the pulmonary 

 artery and the upper part of the anterior portion of the right 

 ventricle. A line of fat, in which lie the interventricular branch 

 of the left coronary artery and the accompanying vein, indicates 

 the position of the septum between the left and right ventricles 

 (Fig. 14). 



After the dissection is completed and the dissectors have 

 carefully noted the relative positions of the various structures 

 which have been exposed, they should proceed to study the lungs. 



Pulmones. The lungs are two comparatively light organs 

 placed one on each side of the mediastinum. They are soft 

 and spongy in texture, and if a small portion is pressed 

 between the fingers and thumb a peculiar sensation called 

 crepitation is felt, as the contained air is forced from one 

 part to another. The ground colour of the surface of the 

 adult lung of town-dwellers is slate-blue, but it is mottled 

 with patches and fine lines of black, caused by deposited 

 carbon particles. The lungs of children are of a yellowish- 

 pink colour, similar to the colour of the lungs of healthy 

 sheep. 



The elasticity of the healthy lung substance is remarkable, 

 but the student will not be able to demonstrate it in a lung 

 hardened by formalin or injured by disease. He can, how- 

 ever, obtain from a butcher the fresh lungs of a sheep, and 

 then, by inflating them through the trachea with the aid of 

 a bellows, he will have no difficulty in satisfying himself of 

 their elasticity. If, in the thorax under dissection, the lungs 



