406 



STRUCTURE OF THE 



[sect. 187. 



Fig. 168. 



surrounded, from its commencement onwards, by Malpighian cor- 

 puscles, and, as may easily be understood, some tubules separate 

 from the bundle earlier, others later, in order to arrive at their 

 corpuscles. Moreover, every cortical tubule runs, after its origin, 

 in a tortuous direction, then curves backwards; and eventually 

 assumes a direction parallel to the straight tubules of the cortical 

 fasciculus. 



The number of the tortuous tubules corresponds to that of the Malpighian 

 corpuscles, and is, accordingly, in every case very large. According to 

 Buschke, each fasciculus corticalis contains 200 tubules, and each pyramid 

 700 such fasciculi, so that if there are 15 pyramids present, we have more 

 than 2 millions of commencing tubules and Malpighian corpuscles. Since 

 each papilla possesses 500 or more openings, it is possible that every cortical 

 fasciculus arises from a single Bellinian tubule ; in every case, it is observed, 

 that on every straight tubule, the divisions are at least ten times repeated. 



§ 187. The tubuli uriniferi are composed everywhere of essen- 

 tially the same elements, viz., a membrana propria and a pavement 

 epithelium. The former is a perfectly structureless envelope, 

 transparent and thin (0-0004'" to o'00o6'"), but still firm and elastic. 

 It can be isolated to a very considerable extent, 

 especially from the straight tubules, and is then 

 apt to become disposed in folds, which often give 

 rise to a striped appearance like connective tissue. 

 Upon the inner side of the envelope, which quite 

 agrees in its chemical , characters with the sarco- 

 lemma (see § 77), there lies a simple layer of 

 polygonal cells of moderate thickness around the 

 cavity of the tubules; these are very prone to 

 become altered, a circumstance which has given 

 rise to many incorrect ideas of the structure and 

 contents of the uriniferous tubules. That is to 

 say, in the ordinary method of investigation in 

 water, they become dilated, distended and pale 

 from absorption of the liquid, so that their poly- 

 gonal form and regular arrangement is effaced, 

 and the renal tubules within the structureless coat 

 appear quite filled with large roundish cells, and 

 no longer present any cavity. Frequently, also, 

 the cells burst, and then the tubules contain 

 nothing but a finely-granular mass with nuclei 

 and clear drops of albumen which has passed out 

 The same alterations take place spontaneously in 



Two straight uri- 

 nary tubules of man, 

 the one with com- 

 plete epithelium, the 

 other half empty, a. 

 membrana propria ; 

 b. epithelium. 



of the cells. 



