THE KIDNEYS 1215 



mesodermal tissue in the phallus; they are at first dense structures, but later 

 vascular spaces appear in them, and they gradually become cavernous. 



The prepuce in both sexes is formed by the growth of a solid plate of ectoderm 

 into the superficial part of the phallus; on coronal section this plate presents the 

 shape of a horseshoe. By the breaking down of its more centrally situated cells 

 the plate is split into two lamella?, and a cutaneous fold, the prepuce, is liberated 

 and forms a hood over the glans. "Adherent prepuce is not an adhesion really, 

 but a hindered central desquamation" (Berry Hart, op. cit.). 



The Urethra." As already described, in both sexes the phallic portion of the 

 cloaca extends on to the under surface of the cloacal tubercle as far forward as the 

 apex. At the apex the walls of the phallic portion come together and fuse, the 

 lumen is obliterated, and a solid plate, the urethral plate, is formed. The remainder 

 of the phallic portion is for a time tubular, and then, by the absorption of the 

 urogenital membrane, it establishes a communication with the exterior; this open- 

 ing is the primitive urogenital ostium, and it extends forward to the corona glandis. 



In the female this condition is largely retained; the portion of the groove on the 

 clitoris broadens out while the body of the clitoris enlarges, and thus the adult 

 urethral opening is situated behind the base of the clitoris. 



In the male, by the greater growth of the pelvic portion of the cloaca a longer 

 urethra is formed, and the primitive ostium is carried forward with the phallus, 

 but it still ends at the corona glandis. Later it closes from behind forward. Mean- 

 while the urethral plate of the glans breaks down centrally to form a median 

 groove continuous with the primitive ostium. This groove also closes from behind 

 forward, so that the external urethral opening is shifted forward to the end of 

 the glans. 



THE URINARY ORGANS. 



The urinary organs comprise the kidneys, which secrete the urine, the ureters, 

 or ducts, which convey urine to the urinary bladder, where it is for a time retained ; 

 and the urethra, through which it is discharged from the body. 



The Kidneys (Renes). 



The kidneys are situated in the posterior part of the abdomen, one on either side 

 of the vertebral column, behind the peritoneum, and surrounded by a mass of fat 

 and loose areolar tissue. Their upper extremities are on a level with the upper 

 border of the twelfth thoracic vertebra, their lower extremities on a level with the 

 third lumbar. The right kidney is usually slightly lower than the left, probably 

 on account of the vicinity of the liver. The long axis of each kidney is directed 

 downward and lateralward; the transverse axis backward and lateralward. 



Each kidney is about 11.25 cm. in length, 5 to 7.5 cm. in breadth, and rather 

 more than 2.5 cm. in thickness. The left is somewhat longer, and narrower, than 

 the right. The weight of the kidney in the adult male varies from 125 to 170 gm., 

 in the adult female from 115 to 155 gm. The combined weight of the two 

 kidneys in proportion to that of the body is about 1 to 240. 



The kidney has a characteristic form, and presents for examination two surfaces, 

 two borders, and an upper and lower extremity. 



Relations. The anterior surface (fades anterior) (Figs. 1120 and 1122) of 

 each kidney is convex, and looks forward and lateralward. Its relations to 

 adjacent viscera differ so completely on the two sides that separate descriptions 

 are necessary. 



Anterior Surface of Right Kidney. A narrow portion at the upper extremity is in 

 relation with the right suprarenal gland. A large area just below this and involv- 

 ing about three-fourths of the surface, lies in the renal impression on the inferior 





