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Henry Gray (1825–1861).  Anatomy of the Human Body.  1918.
 
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 lamellæ, 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 opening 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. Meanwhile 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.
 
3b. 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.

1. 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 (facies 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 involving about three-fourths of the surface, lies in the renal impression on the inferior

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