994 DEVELOPMENT OF URINARY ORGANS. 



dark oval masses, situated behind the upper part of the Wolffian bodies, which are 

 still large and completely hide the kidneys. Though at first smooth and oval, the 

 kidneys soon assume their characteristic general outline, and about the tenth week 

 are distinctly lobulated. The separate lobules, generally about fifteen in number, 

 gradually coalesce in the manner already described ; but at birth, indications of the 

 original lobulated condition of the kidney are still visible on the surface, and the entire 

 organ is more globular in its general figure than in the adult. The kidneys are then 

 also situated lower down than in after-life. 



The formative blastema of the kidney, as observed by Eathke in the foetal calf, 

 soon contains a series of club-shaped bodies which have their larger ends free and 

 turned outwards, and their smaller ends or pedicles directed inwards towards the 

 future hilus, where they are blended together. As the organ grows these bodies 

 increase in number, and finally, becoming hollow, form the uriniferous tubes. At 

 first, short, wide, and dilated at their extremities, the tubuli soon become elongated, 

 narrow, and flexuous, occupying the whole mass of the kidney, which then appears 

 to consist of cortical substance only. At a subsequent period, the tubuli nearest the 

 hilus become straighter, and thus form the medullary substance. The tubuli, as 

 shown by Valentin, are absolutely, as well as relatively, wider in the early stages of 

 formation of the kidney. The Malpighian corpuscles have been seen by Eathke in 

 a sheep's embryo, the kidneys of which measured only two and a half lines in length. 



With regard to the mode of the first appearance of the pelvis and ureter, the state- 

 ments of embryologists are very conflicting. The ureters, it is stated by Eathke, 

 commence after the kidneys, and then become connected with the hilus of each organ, 

 and with the narrow ends of the club-shaped bodies in its interior. At first, according 

 to him, the growing tubuli do not seem to communicate with the cavity of the ureter; 

 but, subsequently, when the wide upper portion of this canal or pelvis of the kidney 

 has become divided to form the future calyces, the pencil-like bundles of the tubuli open 

 into each subdivision of the ureter, and give rise at a later period to the appearance 

 of the papillae and their numerous orifices. The lower ends of the ureters soon come 

 to open into that part of the sac of the allantois which afterwards becomes converted 

 into the bladder. The researches of Mliller and Bischoff are in general confirmatory 

 of Eathke's account. Valentin believes that the ureter (which he has seen at the 

 earliest periods), the pelvis of the kidney, and the uriniferous tubules, are formed in a 

 general blastema, independently of one another ; and that, each part first becoming 

 separately hollowed out, their cavities afterwards communicate with each other. 

 BischofF states that the ureters appear at the same time as the kidneys, and are 

 formed in continuity with the uriniferous tubules, and moreover that all these parts, 

 which are at first solid, are excavated, not separately, but in common, in the farther 

 progress of development. Lastly, according to .Eemak's observations on the chick, 

 the kidneys of that animal commence as two hollow projections from the cloaca, 

 internal to the ducts of the Wolffian bodies, which afterwards elongate and ramify so 

 as to form both the ureters and kidneys. 



In the advanced foetus and in the new-born infant, the kidneys are relatively larger 

 than in the adult, the weight of both glands, compared with that of the body, being, 

 according to Meckel, about one to eighty at birth. 



The Suprarenal Bodies. These organs have their origin from blastema, inde- 

 pendent both of the kidneys and of the Wolffian bodies. Valentin describes them as 

 originating in a single mass, placed in front of the kidneys, and afterwards becoming 

 divided. Meckel has also seen them partially blended together, Miiller has found 

 the suprarenal bodies in contact, but not united. BischofF has always seen them 

 separate, and in early conditions closely applied to the upper end of the Wolffian 

 bodies. Kolliker has also observed them united by a bridge of substance, in which 

 the splanchnic nerves were lost. Prom all this it is plain that the solar plexus and 

 suprarenal capsules are closely united in the early foetal state but it by no means 

 follows that they have a common origin. 



In quadrupeds the suprarenal bodies are at all times smaller than the kidneys ; 

 but in the human embryo they are for a time larger than those organs, and quite 

 conceal them. At about the tenth or twelfth week, the suprarenal bodies are smaller 

 than the kidneys ; at birth the proportion between them is 1 to 3, whilst in the 

 adult it is about 1 to 22. They diminish in aged persons. 



