516 



MANUAL OF HISTOLOGY. 



But HeMs work on the subject, besides elucidating much that was 

 most useful, led to incorrect conclusions as to the structure of the cortex. 

 it served, however, a great purpose in provoking a series of farther inves- 

 tigations, and thus through individual exertions the views on the struc- 

 ture of the organ have undergone since a most salutary change. 



REMARKS. (1.) Among the older essays on the subject which may be said to 

 extend up to the year 1862, we shall only mention, beside the German works of Ger- 

 lack, Litdwig, and Koelliker, those of Bowman in the Phil, Trans. Act. for the year 

 1842, pt. i. p. 57, and Johnstons article "Ecu" in the Cyclopedia vol. iv. p. 231. 



270. 



Turning now to the medullary pyramids, whose apices have received 

 the names of papillce renales, we find the latter studded with the open- 

 ings of the excretory canals. The number of these oval orifices for each 

 papilla is from 10 to 30. They correspond to a 

 similar number of trunks of the gland tubes (fig. 

 508, a). The latter are, however, very short, and 

 almost in the immediate neighbourhood of then- 

 mouths each begins to divide usually at very acute 

 angles into two or three branches. These again 

 split up into several more (b, c, d, e) until the 

 whole assumes the appearance of a bunch of twigs. 

 In the most peripheral groups in the human 

 kidney each tube presents to a certain extent the 

 appearance of a runner with somewhat knotted 

 branches creeping for a greater or less distance 

 along the ground (Henle). 



With this rapid sub-division the canals become 

 considerably narrower. While the mouths and 

 primary trunks possess a calibre of '3-0 '1985 

 mm., the diameter even of the first series of 

 branches sinks to O'l 985-0*0990 mm., and in the 

 next in order to 0'0510-0'501 mm. This is the 

 diameter of the uriniferous tubes at about two 

 lines from the apex of the papillae, and which 

 they continue to maintain throughout the rest of 

 their slightly divergent course through the medul- 

 lary substance. Further division is now no longer remarked, or if seen 

 is only exceptional. 



The increase in bulk of the medullary pyramids towards the cortical por- 

 tion of the organ is partly explained by this division and subdivision of the 

 uriniferous tubes, but only partly so. Another factor in this enlargement 

 of the bases of the pyramids is the system of narrow, looped, uriniferous 

 tubes (Henle), which appear here in addition to those opening at the 

 papillae, and to which the name of canals of Henle has been given (Koelliker). 

 These, from 0'04, to OO2 mm. in diameter, pass in great numbers out of 

 the cortex into the medullary portion, and are here doubled back upon 

 themselves sooner or later (i.e., at a greater or less distance from the 

 papillae), forming regular loops. Thus they return to the cortex, becoming 

 wider in their course back again. In order now to prevent all misun- 

 derstanding in the rather complicated explanation of the arrangement of 

 parts about to follow, we shall apply to those limbs of the looped canals 



Fig. 508. A uriniferous tube 

 with its branches from the 

 medullary substance of a 

 new-born kitten's kidney 

 (prepared with hydro- 

 chloric acid), a-e, divisions 

 from the first to the fifth 

 order (original drawing 

 from Schujeigger-Seidel). 



