chap, xxx.] KIDNEY, URETER, AND BLADDER. 233 



The papillary portion is uniformly and longi- 

 tudinally striated. 



Tracing a medullary ray from the boundary layer 

 into the cortex, it is seen that its breadth gradually 

 diminishes, and it altogether ceases at a short distance 

 from the outer capsule. A medullary ray is, con- 

 sequently, of a conical shape, its apex being situated 

 at the periphery of the cortex, its base in the 

 boundary layer. Such a pyramid is called a pyramid 

 of Ferrein. 



304. All urinary tubules commence as convoluted 

 tubules in the part of the cortex named the 

 labyrinth, but not in the medullary rays, with a 

 csecal enlargement called a Malpighian corpuscle, and 

 terminate having previously joined with many other 

 tubules into larger and larger ducts at one of the 

 many minute openings or mouths at the apex of a 

 papilla. On their way the tubes several times alter 

 their size and nature. 



From its start to its end there is a continuous 

 fine membrana propria forming the boundary wall 

 of the urinary tubule, and this membrana propria is 

 lined with a single layer of epithelial cells differing in 

 size, shape, and structure from place to place; in 

 the centre of the tubule is a lumen, differing in size 

 according to the size of the tubule. 



305. (1) Each Malpighian corpuscle (Fig. 134) 

 is composed of the capsule the capsule of Bowman 

 and the glomerulus, or Malpighian tuft of capillary 

 blood-vessels. 



A, Cortex limited on its free surface by the capsule ; a, subcapsular layer not 

 containing Malpighian corpuscles; a', inner stratum of cortex without 

 Malpighian corpuscles; B, boundary layer; c, papillary part next the 

 boundary layer; 1, Bowman's capsule : 2, neck of capsule : 3, proximal con- 

 voluted tube ; 4, spiral part ; 5, descending limb of Henle's loop-tube ; 6, 

 the loop itself ; 7, 8, and . the ascending limb of Henle's loop-tube ; 10, the 

 irregular tubule ; 11, the distal convoluted tubule; 12, the first part of the 

 collecting tube ; 13 and 14, larger collecting tube ; in the papilla itself, not 

 represented here, the collecting tube joins others, and forms the duct. 

 (Atlas.) 



