chap. xxx. j KIDNEY, URETER, AND BLADDER. 231 



the surface of the papilla? (facing the calices) there 

 is a continuous layer of fibrous tissue, and this on 

 its free surface is covered with stratified transitional 

 epithelium. 



The parenchyma of the kidney consists entirely of 

 the urinary tubules and the intertubular blood-vessels, 

 and there is an interstitial or intertubular connective 

 tissue framework in the shape of honeycombed hyaline 

 membranes with flattened nucleated branched or 

 spindle-shaped cells. The meshes of the honeycomb 

 are the spaces for the urinary tubules and blood- 

 vessels. 



302. B. The parenchyma. I. The urinary 

 tubules (Fig. 133). In a transverse or longitudinal 

 section through the kidney we notice the cortex, the 

 boundary layer of Ludwig and the papillary portions, 

 the last terminating in the conical papillce in the cavity 

 of the calices. 



The boundary layer and the papillary portion 

 form the medulla. A papilla with the papillary 

 portion and boundary layer, continuous with it, con- 

 stitute a Malpighian pyramid. The relative propor- 

 tion of the thickness of the three parts is about 3 '5 

 cortex, 25 boundary layer, and 4 papillary portion. 



303. The cortex consists of vast numbers of con- 

 voluted tubules with their caecal origin, the Mal- 

 pighian corpuscle ; this is the labyrinth separated into 

 vertical divisions of equal breadth by regularly disposed 

 vertical straight striae originating a short distance from 

 the outer capsule, and radiating towards the boundary 

 layer which they enter. Each of these striae is a bundle 

 of straight tubules, and represents a medullary ray. 

 The boundary layer shows a uniform longitudinal stria- 

 tion, in which opaque and transparent striae alternate 

 with one another. The opaque striae are continuations 

 of the medullary rays, the transparent striae are 

 bundles of blood-vessels. 



