164 THE URINARY ORGANS. 



pighian bodies are all situated in the interpyraraidal portions 

 of the cortex, which they stud as prominent granular points. 

 The arrangement of the Malpighian body is adapted to 

 secretory action ; the expanded glomerulus affords a large 

 surface over which fluid may transude from the blood cir- 

 culating in the capillaries into the cavity of the capsule and 

 uriniferous tubule. The slightly smaller size of the efferent 

 vessel is explainable on the ground that the blood entering 

 by the afferent vessel loses a portion of its fluid through the 

 walls of the glomerulus. 



The neck of the uriniferous tubule is a constricted portion 

 at the junction of the Malpighian body with the proximal 

 convoluted tubule. At this point the squamous cells of the 

 capsule of Bowman become thicker and merge into the 

 cuboidal cells that line the convoluted tubule. 



The proximal convoluted tubule, the first portion of the 

 uriniferous tube, is much twisted, contorted, and bent. It is 

 lined with a single layer of columnar or spheroidal epithe- 

 lium-cells, which are striated toward their attached bases ; 

 these cells are opaque, granular, somewhat irregular in shape 

 and unequal in size, and of glandular type. The proximal 

 convoluted tubules have a greater calibre than most portions 

 of the uriniferous tubules; they are situated in the inter- 

 pyramidal portions of the cortex, are surrounded by abundant 

 capillaries, and are active secretory portions of the tubules. 



The spiral tubule is the term applied to the portion of the 

 uriniferous tubule that succeeds the proximal convoluted por- 

 tion. It is straighter than the latter, having only a slight 

 spiral twist, and lies in a pyramid of Ferrein, passing down to 

 the medulla. It is lined with simple columnar epithelium 

 resembling that of the convoluted tubule, but rather lower 

 and less striated. 



The descending limb of Henle's loop begins at the junction 

 of the cortex and medulla, where the spiral tubule merges 

 into it, and lies in a Malpighian pyramid, passing downward 

 to the loop of Henle. At the latter point the uriniferous 

 tubule makes a sharp U-shaped bend on itself, turning upward 

 in an ascending limb. 



The descending limb is a straight, narrow tube lined with 

 a single layer of flattened or lenticular epithelial cells, the 



