PHYSIOLOGICAL ANATOMY OF THE KIDNEYS. 



397 



into the pyramids, returning to the cortical substance in the form of loops. This ar- 

 rangement will be fully described in connection with the cortical substance. 



The tubes of the pyramidal substance are composed of a strong, structureless base- 

 ment-membrane, lined with granular, nucleated cells. According to the researches of 

 Bowman, the tubes measure from ^-Q- to -^-^ of an inch in diameter at the apices, and 

 near the bases of the pyramids their diameter is about -^ of an inch. The membrane 

 of the tubes is dense and resisting, and portions of it with the epithelial lining removed 

 can generally be seen in microscopical examinations, when the pyramidal substance has 

 been simply lacerated with needles. This membrane is from -^fo^ to FFCW f an inch 

 in thickness. 



The cells lining the straight tubes exist in a single layer applied to the basement- 

 membrane. They are thick, irregularly polygonal in shape, and contain numerous albu- 

 minoid granules. They present one, and occasionally, though rarely, two granular nuclei, 

 with one or two nncleoli. They are very liable to alteration and are only seen in the 



FIG. 114 (A). Longitudinal section of the^pyram- 

 idal substance of the kidney of the foetus. 

 (Sappey.) 



1, trunk of a lasge urinifcrous tube ; 2, 2, primary 

 branches of this tube ; 3, 3, 3, secondary branches ; 

 4, 4, 5, 5, 6, 6, 7, 7, 7, 7, branches becoming smaller 

 and smaller ; 8, 8, 8, 8, loops of the tubes of Henle. 



normal condition in a perfectly fresh, healthy kidney. Their diameter is about 

 an inch. The caliber of the tubes is reduced by the thickness of their lining epithe- 

 lium to TfifK or T^rff of an inch. 



FIG. 114 (B). Longitudinal section of the cortical sub- 

 stance of the same kidney. (Sappey.) 

 1, 1, limit of the cortical substance and base of the pyra- 

 mids ; 2, 2, 2, tubes passing toward the surface of the 

 kidney ; 3, 3, 3, 8, 8, 8, convoluted tubes ; 4, 4, 4, 4, 5, 

 Malpighian bodies ; (5, 6, artery, with its branches (7, 7, 

 7) ; 9, 9, fibrous covering of the kidney. 



