. Animal physiology. Physiology, Comparative; Physiology, Comparative. 278 STRUCTURE OF this we have a remarkable example in the Kidney of the higher animals, which is entirely composed of such tubes, and of the blood-vessels distributed amongst them. If we make a vertical section of the kid- ney of Man or any of the higher Mam- malia, (Fig. 159, A) we find that it seems composed of two different substances, one surrounding the other; to the outer, «, the name of cortical (bark-like) substance has been given; whilst the inner, &, is termed medullary (or pith-like). In the cortical
. Animal physiology. Physiology, Comparative; Physiology, Comparative. 278 STRUCTURE OF this we have a remarkable example in the Kidney of the higher animals, which is entirely composed of such tubes, and of the blood-vessels distributed amongst them. If we make a vertical section of the kid- ney of Man or any of the higher Mam- malia, (Fig. 159, A) we find that it seems composed of two different substances, one surrounding the other; to the outer, «, the name of cortical (bark-like) substance has been given; whilst the inner, &, is termed medullary (or pith-like). In the cortical substance, no definite arrangement can be detected by the naked eye; it chiefly consists of a very intricate network of blood-vessels, surrounding the extremi- ties of the tubes. But in the medullary substance we can trace a regular passage of minute tubes, from the circumference towards the centre. They commence in the midst of the network of blood-vessels (B, «), and then pass down in clusters, nearly in a straight direction, and slightly converging towards each other, until each cluster terminates in a little body, called the calyx or cup, which discharges the fluid it receives into the large cavity of the kidney, termed the pelvis, or basin (A, c). From this it is conveyed away by the ureter, d.—These tubes, like the follicles, are lined with epithelium-cells, wThich are the real instruments in the production of their secretion. 358. That there is nothing in the form of the secreting appa- ratus, however, which determines the peculiar nature of its secre- tion, is evident from this fact,—that, in glancing through the Animal series, we find the same secretion elaborated by glandular structures of every variety of form. Thus, we have seen that the bile is secreted, in the lowest animals in which we can distinguish it, by a number of distinct follicles, as simple in their structure Fig. 159.—Structure of the Kidney of Man. A, vertical section of the kidney, a, cortica
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