438 DISCOVERY REPORTS 



tubules and then bend backwards upon themselves towards the cortex (Fig. 34 C). 

 These medullary capillaries are a common feature of mammalian kidneys. 



The injections of the kidneys failed to reveal a regular venous drainage system within 

 the renculi. Many injected sections showed the interstices of the tubules packed with 

 blood corpuscles, which also extended into the tunica albuginea. Outside the renculi 

 sinuous veins were found running over the outer surface of the tunica albuginea to form 

 the interlobular veins. 



All other authors who have studied the vascular system of the kidney, Beauregard 

 most especially, have found efferent veins exactly corresponding to the afferent arteries 

 leaving the renculi on either side of their pelves. In the present work these were not 

 found either in any foetal or adult kidney. 



THE URINARY DUCT 



The main urinary canal of the kidney runs in the central core of the organ (Figs. 23, 

 24, 25, 26) and receives primary branches from the interlobar septa. These receive 

 secondary branches from the lobules, and these again are made up of the junction of a 

 number of tertiary ducts (calices) from the renculi. Since the primaries occupy the 

 interlobar septa they have a roughly segmental disposition, corresponding to the lobes 

 between which they run. The ducts themselves are composed of tough fibrous tissue, 

 lined by a cubical epithelium continuous with that of the collecting tubes of the renculi 

 and of the calices (tertiary and secondary ducts). 



Mention must be made, however, of a small branch of the urinary duct, the importance 



of which was especially emphasized by Daudt. It was mentioned before that author 



by Hyrtl (1872), who attached no particular significance to it. At the extreme posterior 



end of the kidney in Balaenoptera a small branch runs backwards (Fig. 26) and ventrally 



from the main urinary canal towards the extreme posterior tip of the kidney, receiving 



secondary ducts on its course. In Phocaena phocaena this branch comes off about 



one-third of the length of the kidney from the posterior end, while in Delphinapterus 



and Hyperoodon (Daudt) the forking is more evident and the subsidiary branch, much 



larger than in Balaenoptera and Phocaena, comes off from the main duct in the middle 



of the kidney. These backwardly directed branches, Daudt believes, represent the 



posterior branches of the calix major of the kidneys of other mammals, while the main 



urinary duct represents the anterior calix major of a non-lobulated kidney. Thus the 



process of lobulation of the kidney in the Cetacea has involved the great elongation of 



one branch only of the calix major at the expense of the other. If this is correct the 



hilus must be taken to be represented by the whole of the mesal slit, extending from the 



blood vessels anteriorly to the emergence of the ureter — the junction of the two calices — 



behind. 



THE BLADDER AND URETER 



In the foetus the bladder is represented only as a swelling on the umbilical cord 

 (Figs. 1, 12, 21, 22), in which the umbilicus enlarges to form a cavity with longitudinally 

 folded walls. The vesica urinaria so formed has a fairly flat external surface ventrally 



