STRUCTURE AND FUNCTION OF THE KIDNEYS. 



355 



it now passes vertically downward through the most external part 

 (boundary layer) of the Malpighian pyramid into the more internal part 

 (papillary layer), where it curves up sharply, forming altogether the (5 

 and 6) Loop of Henle, which is a very narrow tube lined with flattened 



FIG. 244. -A Diagram of the sections of uriniferous tubes. A, cortex limited externally by the 

 capsule; a, subcapsular layer not containing Malpighian corpuscles; a' inner stratum of cortex, also 

 without Malpighian corpuscles; B, boundary layer; C, Papillary part next the boundary layer; 1, 

 Bowman's capsule of Malpighian corpuscle; 2, neck of capsule; 3, proximal convoluted tubule; 4, 

 spiral tubule; 5, descending limb of Henle's loop; 6, the loop proper; 7, thick part of the ascending 

 limb; 8, spiral part of ascending limb: 9, narrow ascending limb in the medullary ray, 10, the irreg- 

 ular tubule; 11, the intercalated section, or the distal convoluted tubule; 12, the curved collecting 

 tubule; 13, the straight collecting tubule of the medullary ray; 14, the collecting tube of the boundary 

 layer; 15, the large collecting tube of the papillary part which, joining with similar tubes, forms the 

 duct. (Klein and Noble Smith.) 



nucleated cells. Passing vertically upwards just as the tube reaches the 

 boundary layer (7), it suddenly enlarges and becomes lined with poly- 



