THE ABDOMEN 833 



Another view is that the complicated system of convoluted tubules, just 

 referred to as lying beyond the collecting or excretory tubules, is developed 

 as a ramification of these tubules, just as the collecting tubules are ramifica- 

 tions of the calices. In other words, according to this view the entire system 

 of uriniferous tubules — secretory and excretory — the cahces, the pelvis, and 

 the ureter, spring from one common stem — namely, the renal diverticulum 

 from the caudal end of the Wolffian duct. The blind extremity of a proximal 

 convoluted tubule becomes enlarged, and is invaginated by a tuft of capillary 

 bloodvessels, called a glomerulus; the invaginated bhnd end of the proximal 

 convoluted tubule forms the capsule of Bowman; and the glomerulus and 

 the capsule of Bowman form a Malpighian corpuscle of the kidney. 



The vascular constituents, the interstitial connective-tissue stroma, the 

 columns of Bertini, and the renal capsule are developed from the metanephric 

 blastema. 



The ureter, of either side, which originally opens into the urogenital sinus 

 in common with the Wolffian duct, becomes detached from that duct and 

 opens by an independent orifice into the urogenital sinus on its dorsal cispect. 

 It may here be stated that the urinary bladder is developed from the uro- 

 genital sinus. 



Summary. — The pronephros is functional in lower vertebrates — e.g., certain 

 Fishes, and Amphibia during the larval stage. In Man it is rudimentary. 

 The pronephric duct persists as the mesonephric or Wolffian duct. 



The mesonephros or Wolffian body succeeds to the pronephros, and persists 

 as the functional kidney in Fishes and Amphibia. In Mein it atrophies to a 

 large extent, and is replaced by the metanephros. 



The metanephros is the permanent human kidney. 



THE PELVIS. 



The pelvis is the lower division of the abdomen which lies below 

 the level of the ilio-pectineal lines and sacral promontory. Unhke 

 the abdomen proper the walls of the pelvis are chiefly osseous. 

 The posterior wall is constructed by the sacrum and coccyx, with 

 the origins of the pjTiformes muscles. Each lateral wall is formed 

 by the body and spine of the ischium, and is covered by the 

 obturator intemus muscle. The anterior wall is formed by the 

 bodies of the pubic bones which, in the median line, construct the 

 symphysis pubis. Between the posterior wall and each lateral wall 

 is the large sacro-sciatic space, which is partly closed by the power- 

 ful great and small sacro-sciatic ligaments. This space is divided 

 into two parts by the small sacro-sciatic ligament and the spine of 

 the ischium. The upper part forms the great sacro-sciatic foramen, 

 which transmits the pyriformis muscle, the gluteal vessels and 

 nerves, the sciatic vessels and nerv^es, the internal pudic vessels and 

 pudic nerve, the nerve to the obturator intemus and gemellus 

 superior, and the nerve to the quadratus femoris and gemellus in- 

 ferior. The lower part forms the small sacro-sciatic foramen, which 

 transmits the obturator internus muscle and its nerv-e, the internal 

 pudic vessels, and the pudic ner\'e. At each lateral part of the 

 anterior wall is the obturator foramen, which is closed, except 

 superiorly, by the obturator membrane, covered by the obturator 

 intemus muscle. Below the symphysis pubis is the subpubic arch, 

 which is occupied by the triangular ligament of the urethra. The 



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