110 HUMAN EMBRYOLOGY AND MORPHOLOGY. 



the vessels and glomeruli, and possibly the convoluted tubules, ar 

 derived from the mesoblast of the intermediate cell mass. It wil 

 be remembered that the epithelial lining of the Wolffian duct i 

 epiblastic in origin, and the renal bud which springs from it mus 

 also be of a similar nature. 



The kidney grows forward until it touches the supra-rena 

 bodies. At the same time it undergoes a rotation so that tb 

 hilum, instead of pointing backwards to the pelvis, is directei 

 inwards and forwards. The secretory tubules are grouped ii 

 lobules or pyramids. Up to the time of birth and for somi 

 time afterwards the lobules remain distinct, and this is the per 

 manent condition in mammals, such as the ox, bear, seal, etc 

 In man, with the formation of new cortex beneath the capsule 

 all marks of separation between the surface parts of the rena 

 lobules disappear, only their apices or pyramids remaining 

 distinct. As the renal buds of opposite sides grow forwardE 

 they may come in contact and fuse partially together at thei: 

 caudal extremities. In this way the condition known as horse 

 shoe kidney is produced. The renal bud may subdivide at iti 

 commencement, thus giving rise to two or even three ureters 

 Although the ureters remain distinct, the renal parts commonlj 

 fuse again to form one kidney. 



THE MULLERIAN DUCTS. 



The Miillerian Ducts or Oviducts are present in almost all verte 

 brates, and convey the ova to the surface of the body. In fishes 

 Amphibians, reptiles, birds and lower mammals (Marsupials) thi 

 ducts terminate in the cloaca. This is also the case in thi 

 embryonic stages of man and all higher mammals. The develop 

 ment of the duct in man is very simple (Fig. 85). It is develope( 

 ■on the outer surface of the Wolffian ridge, below (ventral to) tin 

 Wolffian duct, by a tubular invagination of the mesothelium of th< 

 coelom. The anterior (cephalic) end remains connected with tin 

 coelom and forms the ostium abdominale. As it passes back 

 wards in the Wolffian ridge it lies below and internal to thi 

 Wolffian duct and comes in contact with the Miillerian duct o 

 the opposite side in the pelvis (Fig. 87). The Miillerian due 



