lining epithelium, the cells of which by their nuclei are brought into clear relief."

On the other side of Henle's loops, where the diameter of the tubes becomes greater, the epithelium presents the appearance of true cylindrical cells, which are laid over one another as shingles, in a direction from the medulla to the cortex. In the tubuli contorti we find again the same jelly-like arrangement as in the curved tubes leaving the capsula Malpighii. In the straight tubes, even to the ductus papillaris, the epithelium is built up of a single layer of sharply defined cylindrical cells, with their broad bases toward the canal wall and their blunt points toward the lumen. (Pl. I., Fig. A, 1.)

THE BLOOD-VESSELS OF THE KIDNEYS.-The arteria renalis sends the greater part of the blood through the cortex. Its branches penetrate without forming meshes to the limit of the cortex, and here breaks up suddenly into very fine arteries, the arteriola interlobulares and arteriolæ rectæ.

The arteriola interlobulares run between every two medullary rays. Having reached the layer of convoluted tubules, they give off a small branch to each capsula Malpighii. This little branch (vas afferens glomeruli) pierces through the ball-like termination of the urinary canal (according to others, it only presses in), and breaks up here "into a free waving bunch of capillaries (glomeruli), which unite again within the capsule to form a common venous stem, the vas efferens glomeruli." This stem leaves the capsule in the same place

that the vas afferens enters. After the vas efferens leaves the capsule, "it takes its direction toward its own medullary ray, or when this is wanting (as in the outermost layer of the cortex), at once toward the convoluted tubes, where it breaks up into a number of capillaries, forming a network of anastomosing meshes around the tubules." The vasa efferentia communicate by means of capillaries with one another throughout the cortex, and also with the vessels of the medulla, in the same manner.

The arteriola recta, which go from the cortex into the medulla, have their course in the slit-like spaces which lie in the limits of the medulla between the bundles of urinary tubules, and run to the papillæ, in the mean time dividing up into several parallel branches. When these vessels meet the converging bundles of the urinary canals, they break up into capillaries surrounding the urinary tubes, and then are distributed to the surfaces of the papillæ. This network of capillaries communicates with that of the cortex.

From the above-described capillary nets the venous stems arise. In the cortex of the kidney, especially in that layer external to the glomeruli, the union of ve nous stems is star-shaped (venæ stellata). The common venous stem penetrates that part of the cortex endowed with glomeruli and medullary rays, lies alongside of an arteria interlobularis, and receives numerous branches from the cortical network.

The venula recto run in the same clefts with the arteries, and on the border of the medulla unite with

the veins coming from the cortex to form greater stems. The capsule receives its vessels partly from the arteriæ interlobulares, and partly from other arterial stems in the neighborhood, viz., the arteria phrenica, lumbalis, and supra-renalis. Their capillaries run partly into the venæ stellatæ of the cortex and partly into the veins corresponding to the above-mentioned arteries.

THE NERVES of the kidney are supplied by the plexus cœliacus of the sympathetic. Their terminations in the kidney are unknown. They run alongside the great blood-vessels in the same manner as the lymph-vessels which empty into the glands of the groin.

2. THE EXCRETORY DUCTS.

The ureters, pelvis, and calices.have an external fibrous coat, a layer of unstriped muscular fibre, and an internal mucous membrane. The fibrous coat is continued into the tunica albuginea of the kidney, and is composed of ordinary connective and elastic tissue. The muscular coat of the ureters consists of three layers. The innermost is composed of longitudinal fibres, the middle of transverse, while the external and weakest is again made up of longitudinal fibres. In the pelvis the arrangement is the same. In the calices the muscular layers become thinner, and are finally wanting at the borders of the papillæ. The mucous membrane is thin, tolerably vascular, and without glands and papillæ. The epithelium is in layers, and is characterized by the size and form of its elements. The cells in the deep

layer are round and small; in the middle layer they are cylindrical and spherical, and possess prolongations; while in the outer layer they are many-angled and flattened, and vary considerably as regards size. (Pl. I., A, 2.)

The Bladder possesses the same arrangement of layers. The muscular layer is often considerable, but the fibres run so irregularly that a schematic representation is impossible. The internal layer is found to be made up of a network of circular fibres, which form oblique and cross meshes about the neck of the bladder, and are in greatest quantity around its mouth, forming the sphincter vesica. Upon these circular fibres lie the more external muscular fibres, which run in different directions. The trigonum Lieutaudi consists simply of a thickening of the layers of connective tissue extending from the ureters to the caput gallinaginis. The mucous membrane has (except at the trigonum) a dense submucous layer, which is tolerably rich in blood-vessels and nerves, especially at the fundus and neck. In the neck and toward the fundus of the bladder are found glands formed like bunches of grapes, which have a cylindrical epithelium and mucous contents.

The epithelium of the bladder is of several coats, and varies like that of the ureters in its different layers. The innermost, which lines the cavity of the bladder, is composed of cells which show a more flattened appearance, but differ greatly in size and shape. The middle layer is formed of young cells with conical ends turned away from the cavity of the bladder. These prolonged

ends often extend into the deep layer. The deep layer is composed of irregular oval cells, which, as opposed to the middle layer, have their smaller ends in the direction of the cavity of the bladder. (Pl. I., A, 3.) The blood-vessels of the bladder are the arteria vesicalis, superior and inferior, springing from the arteria hypogastrica. These enter the bladder wall at the fundus, piercing the muscular layer in an oblique direction. Here they give off branches, which break up into capillaries in the layer of connective tissue beneath the epithelium. The nerves are found in greatest abundance at the fundus, in the connective tissue of which it is possible to recognize the axis cylinders of their fibres. Their terminations are unknown. The blood-vessels and nerves of the ureters are similar to those of the bladder.

The Male Urethra has a corpus cavernosum with a fibrous coat and loose tissue similar to that of the penis, only much more delicate. It has a glandular organ, the prostata, which supports it. The mucous membrane permits to be seen beneath it a layer of connective tissue, rich in elastic fibres. External to this are transverse and longitudinal smooth muscular fibres, both in the pars prostatica and membranous portion of the urethra.

The epithelium of the male urethra is composed of cylindrical cells (Pl. I., B, 1), but in the forward half of the fossa navicularis we find papillæ and pavement epithelium. The epithelium of the ducts of the accessory glands, as the prostate, Cowper's, and Littre's, and that