. A laboratory manual and text-book of embryology. Embryology. THE METANEPHROS 209 constitute the collecting tubules which form the greater part of the medulla of the adult kidney. When the four to six primary tubules develop, the nephrogenic cap about the primitive pelvis is subdivided and its four to six parts cover the end of each pri- =€ranlcU pole Zubuie Crantat pole tubule Caudal pole tubule Ureter. Tertiary coL- UctittQ tubule Fig. 203.—Diagrams showing the development of the primitive pelvis, calyces and collecting tubules of the metanephros (based on reconstructions by Schreiner and F
. A laboratory manual and text-book of embryology. Embryology. THE METANEPHROS 209 constitute the collecting tubules which form the greater part of the medulla of the adult kidney. When the four to six primary tubules develop, the nephrogenic cap about the primitive pelvis is subdivided and its four to six parts cover the end of each pri- =€ranlcU pole Zubuie Crantat pole tubule Caudal pole tubule Ureter. Tertiary coL- UctittQ tubule Fig. 203.—Diagrams showing the development of the primitive pelvis, calyces and collecting tubules of the metanephros (based on reconstructions by Schreiner and Felix). mary tubule. As new orders of tubules arise, each mass of nephrogenic tissue increases in amount and is again sub- divided until finally it forms a peripheral layer about the ends of the branches tributary to a primary tubule. The converging branches of such a tubular "tree" constitute a primary renal unit, or pyramid, with its base at the periphery of the kidney and its apex projecting into the pelvis. The apices of the pyramids are termed renal papilla and through them the larger collecting ducts open. The nephrogenic tissue forms the cortex of the kidney, and each sub-division of it, covering the tubules of a pyramid peripherally, is marked off on the surface of the organ by grooves or depressions. The fetal kidney is thus distinctly lobated, the lobations persist- ing until after birth. The primary pyramids are subdivided into several secondary and tertiary pyramids. Between the pyramids the cortex of nephrogenic tissue dips down to the pelvis, forming the renal columns (of Bertini). The collect- 14. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Prentiss, Charles William, 1874-1915. Philadelphia, London, W. B. Saunders
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