From the summits of the pyramids extend great numbers of very small tubes which, by branching, penetrate to all parts of the kidneys. These are the _uriniferous tubules_, and they have their beginnings at the outer margin of the kidney in many small, rounded bodies called the _Malpighian capsules_ (_A_, Fig. 88). Each capsule incloses a cluster of looped capillaries and connects with a single tubule (Fig. 89). From the capsule the tubule extends toward the concave side of the kidney and, after uniting with similar tubules from other parts, finally terminates at the pyramid. Between its origin and termination, however, are several convolutions and one or more loops or turns. After passing a distance many times greater than from the surface to the center of the kidney, the tubule empties its contents into the expanded portion of the ureter. [Fig. 88] Fig. 88—*Sectional view of kidney.* 1. Outer portion or cortex. 2. Medullary portion. 3. Pyramids. 4. Pelvis. 5. Ureter. _A._ Small section enlarged to show the tubules and their connection with the capsules. [Fig. 89] Fig. 89—*Malpighian capsule* highly magnified (Landois). _a._ Small artery entering capsule and forming cluster of capillaries within. _e._ Small vein leaving capsule and branching into _c_, a second set of capillaries, _h._ Beginning of uriniferous tubule. The uriniferous tubules are lined with secreting cells. These differ greatly at different places, but they all rest upon a basement membrane and are well supplied with capillaries. These cells provide one means of separating wastes from the blood (Fig. 90). [Fig. 90] Fig. 90—*Diagram illustrating renal circulation.* 1. Branch from renal artery. 2. Branch from renal vein. 3. Small artery branches, one of which enters a Malpighian capsule (5). 6. Small vein leaving the capsule and branching into the capillaries (7) which surround the uriniferous tubules. 4. Small veins which receive blood from the second set of capillaries. 8. Tubule showing lining of secreting cells.