THE URINARY ORGANS 319 



about 2 inches apart when the bladder is moderately 

 distended. The trigone is a smooth, triangular surface, 

 paler than the rest of the mucous membrane. It is 

 bounded at the basal angles to the orifices of the ureters, 

 and the apex to the internal urethral orifice. The 

 ureteral folds are the prolongations extending beyond 

 the ureteral orifices, of the transverse ureteral fold 

 containing muscle fibers covered by the mucous 

 membrane. The internal urethral openings is sur- 

 rounded by a circular fold of mucous membrane, 

 called the annulus urethalis. 



The ligaments of the bladder are: true and false. 

 The true are the two anterior, two lateral, and the 

 urachus. The false are five, and consist of folds of 

 peritoneum. 



Method of Urine Secretion. The urine contains 

 the waste products resultant from body metabolism 

 which are eliminated through the kidneys, ureter, 

 bladder, and urethra. 



Several theories have been demonstrated in regard 

 to how these waste products pass from the blood to 

 the urine. However, the two accepted methods of 

 urine secretion or excretion are based on the principles 

 of filtration and secretion. 



The uriniferous tubules as described above com- 

 mence as the capsule of Bowman, which surrounds 

 a collection of capillaries (glomerulus) . Bowman's 

 capsule is simply an indentation of the tubule. It 

 consists of two walls, an outer one covered with 

 flattened epithelium resting on a very thin basement 

 membrane, and an inner wall consisting of flattened 

 epithelium which is reflected over and encloses the 

 glomerulus. Thus the blood in the capillaries is 

 separated from the interior of Bowman's capsule 

 by the intervention of the capillary wall and the 

 inner layer of epithelium, lining the inner wall of the 

 capsule. The secretion of urine primarily takes 



