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HANDBOOK OF PHYSIOLOGY. 



a nearly homogeneous membrane, and are lined internally by epithelium. 

 They vary considerably in size in different parts of their course, but are, 

 on an average, about -$fo of an inch ( mm.) in diameter, and are found 



Fig. 289. A diagram of the sections of uriniferous tubes. A, Cortex lim^-ed externally by the 

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

 also without Malpighian capsules ; B, boundary layer; C, papillary part next .Mie 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 ir- 

 regular tubule; 11, the intercalated section, or the distal convoluted tubule; 12, thi curved collect- 

 ing 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 

 lubes, forms the duct. (Klein.) 



to be made up of several distinct sections which differ from one another 

 very markedly, both in situation and structure. According to Klein, 

 the following segments may be made out: (1) The Malpighian corpus- 



