STKUCTURE OF THE KIDNEY. 543 



the latter is a layer of loose areolar tissue abounding in fat-cells, 

 improperly termed the adipose capsule. The structure of the kid- 

 ney is, therefore, but the repetition of that of each lobule. 



Each lobule is of a pyramidal form, the base presenting on the 

 surface of the kidney, and the apex at the Tiilu-s; the outer por- 

 tion, about half an inch thick, being more vascular, and constituting 

 the cortical portion of the kidney, while the remaining part con- 

 tains no Malpighian bodies, but consists principally of the urinifer- 

 ous tubes, and is termed the medullary or tubular portion. The 

 vascular portion, however, also gives off processes inward, ex- 

 tending even to the hilus (the columns of Bertini). 



1. The tubuli uriniferi of the kidney commence in the papillae of 

 each lobule (i. e. the prominent part constituting the apex of the 

 lobule), by from 200 to 500 orifices -g^ to yj^ of an inch in dia- 

 meter, scattered over its surface; and traverse the pyramids in close 

 contiguity (tubes of Bellini). Each tubule in its course divides at 

 least as many as ten times, and usually at very acute angles, into 

 two, or more rarely into three or four smaller branches, diverging 

 from each other, somewhat like the dentinal tubuli ; and thus giving 

 a greater diameter to the lobules towards the exterior. Vessels 

 are also interpolated between them at regular distances as they pro- 

 ceed outwards. Arriving in the cortical substance they become 

 curved in their course (tubuli contorti}, appearing at first sight to be 

 inextricably interwoven, but ultimately terminating, as discovered 

 by Bowman, 1 in a dilated extremity yaVflW an i ncn i n diameter, 

 containing a vascular plexus of a peculiar kind the Malpighian 

 tody. (Figs. 375, 130, and 377.) 



The tubuli contorti (or convoluted portions of the tubes) are, how- 

 ever, actually arranged in columnar masses ^ to ^ of an inch wide 

 (the pyramids of Ferrein), extending through the entire cortical 

 substance; and here they freely anastomose with each other. The 

 number of the tubuli contorti corresponds with that of the Mal- 

 pighian bodies. Huschke calculates that each " pyramid of Fer- 

 rein" contains 200 tubuli, and that there are 700 of these pyramids 

 in a single lobule, or pyramid of Malpighi. Assigning 15 of the 

 latter to each kidney, it would contain 2,100,000 tubuli contorti, 

 and as many Malpighian bodies. Todd and Bowman maintain 

 that the urine is secreted only in these convoluted portions of the 

 tubes. (Figs. 375, m, and 130, 1 and 2.) 



1 In 1842. 



