CHAPTER XII. 



THE STRUCTURE AND FUNCTION OF THE KIDNEYS. 



The Kidneys are two in number, and are situated deeply in the 

 lumbar region of the abdomen on either side of the spinal column behind 

 the peritoneum. They correspond in position to the last two dorsal and 

 two upper lumbar vertebrae; the right being slightly below the left in 

 consequence of the position of the liver on the right side of the abdomen. 

 They are about 4 inches long, 2 inches broad, and 1% inches thick. The 

 weight of each kidney is about 4-J oz. 



Structure. The kidney is covered by a tough fibrous capsule, which 

 is slightly attached by its inner surface to the proper substance of the 

 organ by means of very fine fibres of areolar tissue and minute blood- 

 vessels. From the healthy kidney, therefore, it may be easily torn on* 

 without injury to the subjacent cortical portion of the organ. At the 

 Mlus or notch of the kidney, it becomes continuous with the external 

 coat of the upper and dilated part of the ureter (Fig. 242). 



On dividing the kidney into two equal parts by a section carried 

 through its long convex border (Fig. 242), the main part of its substance 

 is seen to be composed of two chief portions, called respectively the cor- 

 tical and the medullary portion, the latter being also sometimes called 

 the pyramidal portion, from the fact of its being composed of about a 

 dozen conical bundles of urine tubes, each bundle being called a pyra- 

 mid. The upper part of the duct of the organ, or the ureter, is dilated 

 into what is called the pelvis of the kidney; and this again, after sepa- 

 rating into two or three principal divisions, is finally subdivided into 

 still smaller portions, varying in number from about 8 to 12, or even 

 more, and called calyces. Each of these little calyces or cups, which 

 are often arranged in a double row, receives the pointed extremity or 

 papilla of a pyramid. Sometimes, however, more than one papilla is 

 received by a calyx. 



The kidney is a compound tubular gland, and both its cortical and 

 medullary portions are composed essentially of secreting tubes, the tubuli 

 uriniferi, which, by one extremity, in the cortical portion, end com- 

 monly in little saccules containing blood-vessels, called Malpighian 

 bodies, and, by the other, open through the papillae into the pelvis of the 

 kidney, and thus discharge the urine which flows through them. 



