C. Commencement of the systemic aorta, ascending part of aortic arch.
D. Pericardium investing the heart and the origins of the great bloodvessels.
E. Mediastinal pleura, forming a second investment for the heart, bloodvessels, &c.
F. Costal pleura, seen to be continuous above with that which forms the mediastinum.
G. Vena cava superior, entering pericardium to join V, the right auricle.
H. Upper third of sternum.
I I. First ribs.
K K. Sternal ends of the clavicles.
L. Upper end of sternum.
M. Lower end of sternum.