Varieties

The principal variations of the kidney are as follow :

1. In form. - Disproportionate increase of one or other diameter, producing the long, globular, and discoid types. ;

2. In size. - Inequality : one being small, the other compensatingly large.

3. In number. - The organ may be single, then usually occupying its ordinary position in one or other loin ; or, still more rarely, it may be triple, in which case' the additional gland is either lateral or median. '

4. In position. - One or both kidneys may be above or below the normal level, ^ in the latter and far more frequent case encroaching upon the iliac fossa, or even J entering the true pelvis in front of or behind the rectum ; or the displacement may ! be horizontal, the organ lying upon the vertebral column or even in the opposite loin. |

5. By fusion of the two kidneys ; the union involving the lower extremities only! (' horseshoe kidney '), or the whole length of their inner borders.

6. In mobility. - Undue mobility is usually, if not always, due to a laxity of that portion of the subperitoneal tissue which constitutes the fatty capsule ; but a peritoneal meso-nephron is said to have been seen in extremely rare cases of movable kidney.