160 EXCRETION. 



Summary of the Physiological Anatomy of the ^Kidney. 

 The division of the kidneys into the cortical and pyrami- 

 dal substance is quite apparent to the naked eye. The pyra- 

 mids are distinctly striated, and present, in this regard, and 

 in their darker color, a marked difference from the cortical 

 substance. At the apex of each pyramid there are from two 

 hundred to five hundred little orifices, from -^-^ to yj-g- of 

 an inch in diameter, which connect with the straight tubes. 

 From these openings the tubes branch at a very acute angle, 

 each one leading to a bundle or system of straight canals, 

 forming the collections called the pyramids of Ferrein. The 

 branches of these tubes (the tubes of Bellini) are about -$fa 

 of an inch in diameter, and are composed of a structureless 

 membrane lined by nucleated epithelial cells. 



When these tubes arrive at the bases of the pyramids and 

 pass into the cortical substance, they increase slightly in size, 

 and are lined with granular and rounded cells of epithelium. 

 They then become excessively convoluted, connect with 

 certain other tubes in their course, and after forming loop- 

 like processes extending into the pyramids, finally terminate 

 in rounded or ovoid dilatations (the Malpighian bodies). 

 These dilated extremities measure from -^^ to y-J-g- of an inch 

 in diameter. 



The Malpighian bodies are composed of a fibrous capsule 

 (the capsule of Muller), and each one contains a mass of con- 

 voluted blood-vessels surrounded by nucleated epithelial cells. 



The loop-like processes dip down into the pyramids and 

 return to the cortical substance, present a filamentous, con- 

 stricted portion, and are here called the narrow tubes of 

 Henle. The communicating tubes, which connect these 

 canals with the straight tubes of the pyramidal substance, 

 are sometimes called "intermediate tubes." They are flat- 

 tened or ribbon-shaped, with very delicate walls, and are 

 lined by transparent pavement-epithelium. 



Throughout the kidney there is a delicate stroma of 

 fibrous tissue, in the meshes of which are lodged the blood- 



