CHAP, in.] ELIMINATION OF WASTE PRODUCTS. 667 



the pelvis (columns of Bertini), and also by the larger branches of 

 the blood vessels which, lying outside the pelvis, and dividing as 

 it divides, plunge into the substance of the kidney between the 

 calyces and so between the pyramids, and then run outwards 

 towards the junction of the cortex and medulla to be distributed 

 in a manner which we shall describe presently. The kidney is 

 really, as is seen in the embyro kidney of man and is indicated by 

 the adult kidney of some animals, composed of lobes, each lobe 

 consisting of a more central medulla in the form of a pyramid, 

 covered especially at its base, but also to a certain extent at the 

 sides by cortex, and opening at its apex into an appropriate 

 division of the ureter. As in other glands the larger branches of 

 the blood vessels run in the connective-tissue joining the lobes 

 together, and pass thence into the lobes. In the adult kidney the 

 lobes have become more or less fused together. In the cortex the 

 fusion is complete, but the pyramids still maintain the medulla 

 in a lobed condition, separated however laterally by nothing more 

 than by blood vessels, with a connective-tissue carrying them, and 

 a remnant of cortical substance. The surface of the kidney, save 

 in abnormal cases, shews no indications of division into lobes ; the 

 uniform level of the cortex is bounded by a capsule of connective- 

 tissue, which may be easily stripped off from the cortical substance 

 below, and which at the hilus is continuous with the connective- 

 tissue surrounding and binding together the ureter, renal vessels 

 and renal nerves. A quantity of adipose tissue not infrequently 

 surrounds the kidney, being especially abundant at the hilus. 



394. Each tubule begins as we have said in a Malpighian 

 capsule somewhere in the cortex, either near the capsule or near 

 the base of a pyramid or at some intermediate level. From 

 thence it runs, we have also said, first as a twisted tubule and 

 subsequently as a straight tubule; but in the first part of its 

 course its path is so peculiar that the word twisted does not 

 accurately describe it. Moreover the characters of the tubule 

 change so markedly at various parts of its course, and these 

 changes are probably of such great importance, that a description 

 of the tubule at successive steps of its progress along its whole 

 length becomes advisable, though we at present do not under- 

 stand the meaning of the various changes. As we shall see, 

 some of these complex peculiarities of the mammalian kidney 

 are partly explained by the structure of the kidney of one of the 

 lower animals, such as a frog. It will be convenient to describe 

 first some details of the general course, and to study the changes 

 in character subsequently. 



Leaving the capsule the tubule forms in the neighbouring 

 cortex several sharp but rounded turns, and in this part of its 

 course is very distinctly a twisted, contorted, convoluted tubule. It 

 then, ceasing to be distinctly convoluted, takes on a wavy or 

 gently spiral or sometimes almost straight course, being directed 



432 



