208 



NORMAL HISTOLOGY. 



Malpighian 

 body in 

 labyrinth 



very tortuous and arches towards the free surface as the proximal convoluted 

 tubule ^2); this, after a course of considerable length, usually leaves the 

 labyrinth and enters the medullary ray, which it traverses, somewhat reduced 

 in diameter and slightly winding in course, and passes into the medulla. 

 Immediately upon gaining the latter, the tubule becomes markedly nar- 

 rowed, penetrates the re- 

 apsuie nal pyramid for a variable 



distance towards the pa- 

 pilla, then bends sharply 

 upon itself and retraces its 

 course to enter once more 

 the labyrinth. Its excur- 

 sion into the medulla in- 

 cludes the descending limb 



(3) and ascending limb 



(4) of the loop of Henle. 

 The ascending limb the 

 longer and wider of the 

 parallel limbs of the loop 

 rises within the labyrinth 

 to the immediate vicinity 

 of the corresponding Mal- 

 pighian body and then, 

 after arching over or 

 around the body, gives 

 place to the distal convo- 

 hited tubule (5), a segment 

 which, marked by in- 

 creased diameter and tor- 

 tuosity, crosses the general 

 path of the proximal con- 

 voluted tubule and is suc- 

 ceeded by the narrower 

 arching connecting tubule 

 (6). The latter soon en- 

 ters the medullary ray and 

 joining with similar canals, 

 takes part in forming the 

 straight collecting tubule 

 (7), which, progressively 

 increasing in size by junc- 

 tion with others, traverses 

 the remaining length of 

 the medullary ray and en- 

 ters the pyramid. Within the deeper part of the latter, the collecting 

 tubules fuse into larger and larger canals until, as the relatively wide papillary 

 ducts (8), they terminate at the apex of the papilla at the orifices, fatpapil- 

 lary foramina, which open into the calyces, as the subdivisions of the 

 expanded beginning of the renal duct are called. 



Although as a matter of convenience the entire canal, from its com- 

 mencement at the Malpighian body to its termination on the papilla, has 

 been described as the uriniferous tubule, both genetically and functionally two 

 distinct parts should be recognized. These are (#) the uriniferous tubule 



Labyrinth 



Medullary 

 ray 



FIG. 256. Section of cortex, showing relation of labyrinth to 

 medullary rays. X 50. 



