326 SOLID PARTS OF ANIMALS. 



CHAPTER XXV. 



OF THE KIDNEYS. 



THE kidneys are the important glands which separate the urine 

 from the blood. In man they are two in number, situated close 

 to the spine on each side of the abdomen, just opposite the low- 

 est of the false ribs. They are almost always imbedded in a 

 great quantity of fat. They have a reddish-brown colour, a firm 

 feel, and are about the size of the fist or rather less. Their 

 shape resembles that of a kidney bean. Anteriorly they are co- 

 vered by the peritoneum, which may be easily detached from 

 them. When a kidney is cut across we perceive that it consists 

 of two different substances distinguished from each other by their 

 colour. These from their position are called cortical and me- 

 dullary. 



The cortical substance, placed immediately under the investing 

 membrane, occupies the entire circumference of the organ, be- 

 ing about two lines in thickness, and sends inwards prolongations, 

 between which the medullary portion is placed. It has a deep- 

 red colour, is very easily torn, and consists almost entirely of the 

 capillary terminations of blood-vessels. 



The medullary part consists of a series of conical masses, the 

 bases of which are directed towards the surface of the kidney, and 

 the small extremities towards its fissure. The cones are invest- 

 ed, except at their apex, by the cortical substance. The medul- 

 lary substance is more dense than the cortical, and its colour is 

 much lighter. As it is made up of a series of minute tubes, it 

 is sometimes called tubular substance. 



The fissure of the kidney lodges the renal artery and vein, the 

 nerves and lymphatics, together with the commencement of the 

 excretory duct. This duct, called the ureter, expands opposite to 

 the fissure of the kidney into an irregular oval cavity called the 

 pelvis. The pelvis gives off three tubes, one to each extremity 

 of the organ, and the other to the middle opposite the fissure. 

 Each of these tubes, again, subdivides into from seven to thirteen 

 smaller tubes, each of which terminates in a cup-like cavity cal- 

 led calyx. Each calyx embraces the extremity of one or more 

 rounded processes called papillae ; and each papilla is the summit 



