HUMAN KIDNEY We now proceed to give a detailed account of the anatomy of the human kidney, with such facts in the minute structure of the gland in certain of the lower animals as serve to throw light upon the structure and office of this important organ in man.
Form.—The form of the kidney being so familiar as to serve for a standard of compa rison with 'other objects, it appears needless to speak of its resemblance to a French bean, the concave margin being directed towards the spine, while the convex margin, which is thick and rounded, is directed outwards. The upper extremity is usually broader and thicker than the lower. The anterior surface is convex ; the posterior is flatter and rests upon the muscles and fascia. The two kid neys are occasionally, but very rarely, united by a band of renal substance, extending transversely across the spine in front of the aorta. The two glands thus united have the form of a horse-shoe, the concavity of which is directed upwards.
• Dimensions and weight.—The average length of the kidney is from 4 inches to 41 inches, its breadth 2 inches, and its thickness I inch. Its usual weight is from 3 to 4 ounces.
Position and relations.—The kidneys are situated deeply in the lumbar region on each side of the spine, occupying a space corre sponding to the last dorsal and the two or three upper lumbar vertebrre. The right is usually somewhat lower than the left, being depressed, as it were, by the liver, which is placed just above it. Occasionally one or both kidneys may be found very much out of the natural position, being situated either in front of the spine, or much below the usual posi tion, even as low as the cavity of the pelvis. The kidneys are placed somewhat obliquely, the upper extremities being inclined towards the spine and approaching nearer to each other than the lower. They are imbedded in a layer of adipose tissue, the quantity of which is very variable, being thick and abun dant in fat subjects, while in those vvho have died much emaciated, the loose investment of reticular tissue presents scarcely; a trace of fat.
The anterior surface of each kidney looks somewhat outwards ; it is partly covered by the peritoneum, chiefly at the upper extre mity, and more on the right side than on the left. The right kidney is covered by the ascending colon, and the left by the descending colon. The anterior surface of the right kidney is also in contact with a small portion of the duodenum, and is covered by the right lobe of the liver. In some instances the gall bladder covers a large part of the anterior surface of the right kidney. The left kidney at its upper part lies in contact with the spleen, and is covered by the great end of the stomach when this viscus is distended.
With reference to diagnosis, it is important to bear in mintl the proximity of the kidneys to the colon, and the possibility of disease ex tending from one organ to the other. Ab scess of the kidney has in many instances been known to burst into the colon, and it is not improbable that ulceration of the colon, either simple or malignant, might extend backwards into the kidney.
The posterior surface of the kidney looks somewhat inwards ; it rests upon the quad ratus lumborum muscle, from which it is separated by the anterior division of the tendon of the transversalis ; it is also in contact with the diaphragm, which separates it from the two or three last ribs, and with the psoas muscle, which separates it from the spine.
From a consideration of these relations, it will be seen that exploration of the kidney, with a view to detect enlargement or tender ness, may best be made in the lumbar region on either side. It will also be evident that abscess originating in the kidney may extend backwards, and become diffused amongst the muscles in this region, or that it may approach the surface, and discharge itself by-an opening in the loins. Cases of this kind are known to occur ; and when renal calculi have been the exciting cause of the suppuration, these have escaped through the same opening in the lumbar region.