Before passing on to the description of the minute structure of the kidney, it is de sirable to examine the position of the blood vessels about the medullary cones, so far as this can be ascertained by the unaided eye.
The renal artery, as it enters the hilum of the kidney, breaks up into four or five branches, and these again subdivide, a few of the branches passing behind the pelvis, while the greater number remain in front ; they pass up wards between the calyces enclosed in folds of the fibrous membrane, and so they conne in contact with the sides of the medullary cones. Each cone appears to be supplied by two arterial branches, which, passing up ione on each side, form an anastomosing arch over the base of the cone (fig. 146). From this arterial arch branches proceed in all di rections, the greater number passing into the cortical substance. The venous branches in this situation likewise form arches over the medullary cones, and have the same general arrangement as the arteries ; they unite into four or five trunks which are placed in front of the pelvis. There is no anastomosis be tween the arteries of neighbouring cones ; each medullary cone, with its investing cortical substance, corresponds with one of the sepa rate lobules of the embryo kidney ; and al though in the fully developed human kidney, scarcely any trace of the original lobular division remains, yet the separation of the lobules, so far as their vessels are cohcerned, remains as complete as it is in the perma nently. lobular kidney of the porpoise. When an injection is thrown into the vessels of one lobule, that lobule only is injected, without the transfer of the injection through anastomosing vessels to neighbouring lobules. Obstruction of the artery passing to one lobule will effec tually prevent the injection of that lobule, while the surrounding parts are completely injected. It occasionally' happens during life that the vessels supplying one or two lobules become obstructed, and as a consequence of this obstruction those lobules become atro phied while the rest of the gland is perfectly nourished. Additional evidence of the com
plete isolation of the lobules of the human kidney is afforded by certain other patho logical conditions, which may, with advantage, be briefly alluded to in this place. Eg. 147 represents a section of a kidney, the glan dular structure of vvhich has been destroyed by cysts developed in its substance; the part which remains is a framework or skeleton, con sisting of the capsule (a) continuous below mith the pelvis (b), which is much dilated, while the same fibrous membrane is prolonged continuously through the substance of the kidney to the surface ; the septa (c,c,c), which thus divide the kidney into the various closed which exist in the kidney of the porpoise.* In this instance the tissue has been condensed and thickened by disease. At d, d there may be seen the rounded openings through which the apices of the medullary cones projected into the calyces. The lobulated character of the surface of the same kidney is represented in fig. 148 ; the depressions correspond vvith the fibrous septa, and indicate the position of the original interlobular fissures ; the con vexities correspond- with the lobules, and have been rendered prominent by a liquid accumulation in the closed cavities formed, as above described, in the substance of the organ.t Reference will hereafter be made to some other morbid conditions of the human kidney which have peculiar characters im pressed upon them by these interlobular septa, which are in fact the persistent reniains of that interlobular cellular tissue, which is per manently distinct in certain tribes of mam malia, while in most animals of this class, as in the human subject, it remains as a distinct and easily recognised tissue only during fcetal life. In the completely formed kidney it is blended with and concealed by the surrounding tissues, and manifests its presence as it were indirectly, by the peculiar characters which it impresses on the structure of the kidney as shown by the results of injection or in the course of certain pathological changes.