22 G AETERIAL SYSTEM OF MAN. 



trunk, where it divides into two great branches, which 

 proceed to the lower extremities. From the arch of the 

 aorta are given off the arteries which supply the head and 

 upper extremities. These are, the two carotids, which ascend 

 on either side of the neck; and the two stibclavian, which 

 pass outwards beneath the clavicles, so as to arrive at the 

 arms, becoming successively in their course the axillary and 

 brachial arteries, as they pass through the axilla or arm-pit, 

 and along the arm. The subclavian and carotid arteries of 

 the right side arise together from the aorta, in Man, by a 

 common trunk ; but this arrangement varies much in different 

 Mammals. Thus in the Elephant, the two carotids arise by 

 a common trunk, the two subclavians separately. In some 

 of the Whale tribe, all four are separate. In the Bat, the 

 subclavian and carotid of the left side arise from a common 

 trunk, like those of the right. And in those Euminating 

 animals which possess a long neck, all four arteries come off 

 from the aorta together, by a large trunk, which first gives off 

 the subclavians on either side, and then divides into the 

 carotids. All these varieties occasionally present themselves in 

 Man; a fact of no small interest. 



259. The descending aorta, in its progress along the trunk, 

 gives-off several important branches; as the cceliac, from 

 which the stomach, liver, and spleen are supplied ; the renal, 

 to the kidneys; and the mesenteric, to the intestines. It 

 divides at last into the two iliac arteries ; which, after giving 

 off branches for the supply of the lower bowels, pass into the 

 thighs, where they become the femoral arteries ; and these 

 again subdivide into branches for the supply of the leg. 



260. For the sake of comparison, a figure of the arterial 

 system of a Bird is introduced ; from which it will be seen 

 that by far the larger proportion of its blood is distributed 

 to its upper extremities. In Man, the descending aorta is 

 evidently the continuation of the aortic arch ; and the parts 

 which it supplies receive far more blood than the head and 

 upper extremities, the locomotion of biped man being per- 

 formed almost entirely by his lower limbs. In Quadrupeds, 

 which require nearly as much strength in their fore feet as in 

 their hind, the subclavian arteries bear a larger proportion to 

 the iliac. But in Birds, the function of locomotion is almost 

 entirely performed by the wings ; and their powerful muscles, 



