CIRCULATION OF THE BLOOD. 63 
lie, for the most part, near the surface, which renders them more liable 
to injury ; but the consequences are less serious than in the case of the 
arteries, on account of the less rapid flow of blood. 
The minute vessels which form the connection 
between the smallest branches of the arteries and ~ 
the veins are called the capillaries} from their 
extreme smallness. The figure (55) shews the 
arrangement by which the arteries and veins are 
connected in muscular tissue. 
When the aorta leaves the left ventricle, it rises 
towards the neck, but soon turns downward, form- 
ing a curve called the arch; this trunk passes 
down in front of the spine, and divides into two 
main branches, which proceed to the legs. From 
the arch of the aorta are given off the arteries that 
supply the head and arms with blood: these are 
the two carotid? arteries (c and e, fig. 56), which 
ascend on either side of the neck to the head, and 
the two sub-clavian arteries, which pass beneath 
the clavicles to the arms (the left of these is 
marked g on fig. 56). The descending aorta while 
passing down gives off branch arteries to the 
different parts and organs—the celiac? artery, 
which subdivides into three, to supply the stomach, 
liver, and spleen, one to each kidney, and two to 
the intestines. It at last divides into two branches, 
which supply the legs. 
The veins of the body unite to form two large 
trunks, the superior or descending, and inferior or 
. ascending vena cava,* which meet as they enter the right auricle of the 
heart, f and 8, fig. 54. The descending vena cava.is formed by the union 
of the veins bringing the blood back from the head, the jugular’ veins, 
b and f, fig. 56, and those bringing it from the arms, the sub-clavian veins, 
a@and h. The ascending one brings it back from the legs, the organs 
in the abdomen, and the trunk. The Lesser Circulation will be described 
under Respiration. 











1 From Latin capilla, a hair. 
2 From Greek karod, to stupefy, because a state of torpor is brought on by stopping these 
arteries. 
3 From Latin celia, the belly. 
. #Latin, ‘hollow vein.’ 
5 From Latin yugulum, the hollow at the neck above the collar-bone. 
