34 ANATOMY. 



from which all the arteries of the body are given off: their branches 

 in the neck and elsewhere may be known by their being shaded with 

 cross lines: the continuation of the aorta in the abdomen below the 

 diaphragm, d, is also marked with an asterisk *. The great venous 

 trunks, in which the veins of the body ultimately end, are marked v, 

 which indicates the superior vena cava, receiving the veins of the head, 

 neck, chest-walls, and upper limbs, and v. placed on the inferior vena 

 cava, receiving the veins from the lower half of the trunk, and from 

 the lower limbs, and seen perforating the diaphragm d, to enter the 

 heart. Thus attached, at its base only, by the above-named great 

 bloodvessels, the heart projects forwards and to the left side, so that 

 its point or apex comes near the walls of the chest, between the fifth 

 and sixth ribs, a little to the left of the sternum. The sac of the 

 pericardium, below, adheres to the diaphragm ; at the base of the heart 

 its fibrous layer adheres to the great bloodvessels, but its lining mem- 

 brane or serous layer is reflected upon them, over the surface of the 

 heart, so that this organ, like the lungs, is outside its serous sac, like 

 a man's head thrust into an old-fashioned double nightcap. 



When the heart is removed, as in Fig. 15, it is seen that besides the 

 aorta, a, the thorax also contains the lower end of the trachea, or 

 windpipe, t, which divides therein into two chief branches, called the 

 bronchi, which ultimately ramify throughout the lungs, forming its 

 innumerable air-tubes or bronchial tubes (see Fig. 111). The thorax 

 also contains the longest portion of the gullet or oesophagus, o, which 

 is seen descending from the pharynx, p, supported all along upon the 

 bodies of the vertebrae, and which perforates the diaphragm to enter 

 the abdomen behind the liver, I I', and end in the stomach, s. Besides 

 these parts, there are found in the thorax, the principal absorbent ves- 

 sel in the whole body, or main trunk of those vessels, called the thora- 

 cic duct, which, as shown in Fig. 100, runs up through the thorax, 

 from the abdomen into the neck, resting closely on the vertebral 

 column. Lastly, the thorax also contains portions of the sympathetic 

 nerves, and their branches. These, as shown hereafter in Fig. 64, 

 form a knotted cord on each side of the vertebral column. 



But the chief contents of the thorax are the heart and lungs, the 

 great central organs of circulation and respiration. 



c. The cavity of the abdomen is even less protected by bones than 

 that of the chest, being surrounded by soft parts only, such as broad 

 muscles, tendons, fascia, and skin, excepting behind, where there is 

 the lumbar portion of the spine, and below, where we find the pelvis, 

 the cavity of which may be regarded here as supplementary to, as it 

 is directly continuous with, the abdominal space. Above, the abdomen 

 is as it were roofed in by the vaulted diaphragm, Fig. 14, d. The 

 capacity of the abdomen, as is needed for its contained organs, may 

 vary very much. 



Deeply seated in the abdomen are the great bloodvessels already 

 mentioned, viz., the abdominal aorta* and the inferior vena cava, v r , 

 both giving off, of course, their numerous branches. Quite at the 

 back of this cavity, corresponding with the region of the loins, on each 

 side of the spine, are the two kidneys, of which the left one, seen in 



