114 THB HORSB. 



9 



twenty-three ounces, is shaped Uke a French bean (SEE MANIKIN 

 OF The HORSE) and extends from the loins forward to beneath the 

 heads of the last two ribs. The right kidney (SEE MANIKIN OF 

 The HORSE) is the shape of the heart of cards, and extends from 

 the loins forward beneath the head of the last rib. Each kidney consists 

 of these distinct parts : 



a. The external or vascular part, in which the blood-vessels form 

 elaborate capillary network within the globe-like sac's which form the 

 beginnings of the secreting tubes. 



b. The internal part, made up in the main of the blood-vessels, lymph- 

 atics, and nerves extending between the notch on the inner border of 

 the kidney to and from the outer vascular portion, in which the secretion 

 of urine is almost exclusively carried on. 



c. A large sac-like reservoir in the centre of the kidney into which all 

 the urine tubes empty their secretions. From this reservoir there leads a 

 tube, called the ureter, which carries off the urine to the bladder. There 

 are two of these tubes, one from each of the kidneys, and they open by 

 a valve-closed orifice into the roof the bladder just in front of the neck. 



Action. The arteries which carry the blood to the kidneys are called 

 RENAL arteries, and the veins which carry the blood from the kidneys to 

 the large veins leading to the heart are called renai, veins. The kid- 

 neys do not act constantly but alternate in their action. The blood 

 passes into the kidneys through the arteries, it then reaches the capil- 

 laries of the kidneys which have the power of removing the watery part 

 of the blood containing urea. The blood is then taken up by the small 

 veins and carried to the renal veins. 



Bladder. This is a reservoir which receives the urine from the kid- 

 neys through the arteries, and holds it until the distension is sufficient 

 to cause its voluntary discharge. Circular muscular fibers surround the 

 neck of the bladder which keep it closed, and looped muscles extending 

 in all directions forward from the neck around the unopen end of the 

 bladder empty it by contracting. A dilatable tube (urethra) extends 

 from the neck of the bladder backward on the floor of the pelvis. In the 

 male the urethra extends through the penis to its free end, where it 

 opens through a conical papilla of a pink color. In the full grown 

 female the urethra is nor far from an inch in length, and it is surrounded 

 bj' the circular muscular fibers which closes the neck of the bladder. It 

 opens directly in the middle line of the floor of the vulvas about four and 

 one-half inches from its outside opening. 



