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and blood-vessels. Outside the medullary substance and just under the capsule is the cortex, containing the Malpighian bodies, blood-vessels, and the convoluted tubules or loops of Henle. Each Malpighian body contains within a capsule a plexus of capillaries, the glomerulus, with an afferent arteriole and an efferent vein. The renal artery is a branch of the aorta and the nerves are from the solar plexus.

Fig. 59.—A longitudinal section of the kidney. (Leroy.) a, Renal artery; c, cortex; m, medulla; u, ureter.

Fig. 60.—A Malpighian body or corpuscle. (Leidy.) a, Afferent artery; e, efferent vessel; c, capillaries; k, commencement of uriniferous tubule; h, uriniferous tubule.

The Urine.—As the blood passes through the glomeruli, the urine is filtered off as it were, probably by a process of transudation rather than simple filtration. The cells lining the tubules also play an important part in its formation, not by secreting new substances but by taking up those brought by the blood and discharging them into the convoluted tubules, from which the urine passes through the straight tubules of the medulla to the pelvis, to be carried thence by the ureter. The process of the formation of the urine, there-