Зображення сторінки
PDF
ePub
[ocr errors]

6

480

apex of the cone (where this projects), is called calyx;' its contracting continuation to form the duct is the infundibulum;' the cavity of the gland which it lines, as at p, fig. 479, is the pelvis' of the kidney; the fissure from which it emerges is the hilum.' The renal artery, derived directly from the aorta, fig. 422, d, d, divides into two or three branches on entering the hilum, and, of the subdivisions of these in the medullary substance, the two principal, in the Kangaroo, anastomose to form an arch over the base of the cone, whence proceed the arterioles, fig. 481, a, to the cortical substance. Here the terminal twigs, ib. f, enter the malpighian body, m, to form the vascular brush or tuft; the returning vessel, d, combines, with those from other tufts, e, e, to form the capillary plexus, p, which surrounds the uriniferous tube, t. The capillaries unite to form venules, which on the surface of the human kidney have a stelliform disposition, and when congested give it a finely lobulated appearance. The veins from the centre of each 'star' dip into the renal substance, unite, and ultimately emerge at the hilus' anterior to or ventrad of the artery; but, in a few Mammals, they unite in an arborescent disposition (Felis, Hyana) or form a network (Phoca) upon the surface of the kidney; in all, the venous trunk, fig. 418, k, terminates in the postcaval, ib. v. The uriniferous tubule commences in Mammals, as in lower Vertebrates (vol. ii. p. 538, fig. 356), from the malpighian corpuscle, fig. 481, m, c, and passes toward the surface of the kidney, before being reflected and convoluted in the cortical substance.

[graphic]

Tubuli uriniferi of cortical and medullary parts of kidney. CCLXXXVI.

481

[graphic]

The chief modifications of the kidneys in Mammalia are seen in the shape or absence of the mammilla, and in their composition by a seeming multiplication of simple kidneys, either with or without a common cortical envelope. The first of these is presented by the Ornithorhynchus, fig. 502, a, in which the tubuli uriniferi terminate

Plan of the renal circu'ation

in Mammalia. CXXXVII.

on the concave surface of a small and simple pelvis. The ureter, ib. c, c, takes the usual course to the contracted neck of the bladder, ib. d: but terminates, in the male, in the urogenital canal, below the vasa deferentia; and, in the female, fig. 534, 1, 1, beyond the uterine orifice, m, which thus intervenes between the ureter and the orifice of the urinary bladder. In all respects, save the place of termination of the excretory ducts and their relation to the reservoir of the secretion, the urinary system of the Monotremes adheres closely to the Mammalian type: in the Echidna the mammilla slightly projects. The circumstances in which they deviate from the higher Mammals approximate them to Reptiles; and it is to be observed that the deviation commences where the urinary system begins to be connected with the generative organs, in which the oviparous type of structure is especially manifested.

In the Marsupialia the tubuli uriniferi terminate on a mammilla which projects into the commencement of the ureter in the Opossums, but does not extend beyond the pelvis of the kidney in the Kangaroos. In the larger herbivorous Marsupials the medullary substance forms several lateral abutments to the base of the cone. In Macropus Parryi the kidneys are situated six inches above the brim of the pelvis, and lie in the same transverse line: they have the same relative position in other Poephaga. In the Koala the right kidney is higher by its whole length than the left. In Dasyurus macrurus and D. viverrinus the right kidney lies half an inch higher or in advance of the left; in this carnivorous genus a few branches of the renal veins are distributed upon the surface of the kidney, but not in the same proportion or with the beautiful arborescent disposition characteristic of the kidneys of the Cats, Suricates, and Hyæna. In a Dasyurus macrurus weighing three pounds eight ounces, the two kidneys weighed thirteen drachms. In a Phalangista vulpina, weighing five pounds three ounces, the two kidneys weighed only ten drachms. The ureters terminate, in all Marsupials, at the back of the neck of a large and pendulous urinary bladder, fig. 422, l.

In Hyrax capensis the tubuli uriniferi terminate in a prominent and pointed mammilla; in all the large Perissodactyles, e. g. Horse, Rhinoceros, Tapir, they open upon the concave surface of the renal pelvis, and can be readily injected from the ureter. Injection of the arteries of the Horse's kidney shows the terminal branch, fig. 482, f, dilating within the malpighian corpuscle, d, and there dividing into lobes or groups of capillaries, 1, i; the returning or efferent vessel is shown at 2, e; and the continuation of the uriniferous tubule at 3, t, from the

482

[ocr errors]

capsule of the corpuscle, m.' In the Rhinoceros the pelvis is represented by two longitudinal canals which converge and unite to form the ureter, of which they may be said to be the beginnings. The kidney is lobulated, or composed of numerous renules, each with its cortical and medullary part, but the tubes of the latter unite and converge to open into the longitudinal, quasi pelvic, canals without any valvular prominence.2 The kidney of the Elephant differs chiefly in the termination of the tubuli of the lobes upon slight prominences; of these there is no appearance in the Equide. The tubular divisions of the pelvis are shorter in the Zebra than in the Horse or Ass, where they are continued nearer to the upper and lower ends of the kidneys. The ureters in these, as in the Tapir, terminate as usual in the neck of the bladder. But in Hyrax, concomitantly with an unusual length of loins, the ureters do not reach so far down, but open obliquely into the back part of the fundus vesicæ.'

[graphic]

Malpighan tufts and corpusele: Horse. CXXXVII.

In the Hog-tribe the kidney is simple; but the mammilla is somewhat extended at its free termination. In the Chevrotains and other small ruminants the kidney is simple as in Lissencephala; but in larger deer and antelopes the beginning of a more complex structure is seen in the aggregation of the tubuli uriniferi into several cones, distinct at their bases, but blending into a common elongate or ridge-like mammilla. This structure also obtains in the Camelida; but in the Bovide the cones are distinct, terminate by mammillæ in tubular productions of the renal pelvis, and are associated with some lobes or divisions of the cortical substance, such divisions sometimes including more than one cone.

In the Dugong the tubuli terminate in a single pelvis by several lateral ridges; but the exterior is undivided. In the Manatees, and in Rhytina, according to Steller, the kidney is 2 v". p. 44, pl. 14, figs. 2 and 3.

1 CXXXVII.

lobulated.

In the human kidney the tubuli are grouped into from twelve to fifteen conical bundles, the apices of which project

483

into a common pelvis; but occasionally two cones combine to terminate by a common mammilla: in fig. 483 are shown three cones, in section, with the relative position thereto of the arteries, a, and the veins, b. In the foetus the cortical part is subdivided like the medullary, but the clefts become obliterated in the growth of the kidney.

Quadrumana have a single mammilla; but in the larger kinds it is extended, and the tubuli are partially

[graphic]

the Suricate, Viverride, Hyænas, and Felines is chiefly remarkable for the arborescent disposition the veins

on or near the surface; the mammilla is single, as it is, also, in the Mustelide, Canide, a Suburside. In Bears, Seals, and Whales, the kidney is divided into numerous lobes or renules, in the Walrus amounting to three or four hundred, and in the Porpoise, fig. 427, E, to even a greater number. Each renule has its own capsule, which is removed at a, a, fig. 484; a section of

the renule shows it to be composed of a cortical and medullary

substance, ib. b, c; the tubuli terminate at the apex of a mammilla, d, which projects into an infundibulum. The infundibula are prolonged, and unite to form the ureter which comes out at the medial and hinder surface of the kidney and enters the neck of the urinary bladder.

In most quadrupeds this reservoir is more pendulous, has a more complete covering of peritoneum, than in Man. The oblique valvular course of the ureters through its coats is common to the Mammalian class. The monotremes are the sole exceptions; in them the ureters, fig. 485, 1, 2, do

485

not terminate in the bladder, k, but in the urogenital canal, c, the orifice of the spermduct or oviduct, m, intervening between that of the ureter and the bladder. The urine may dribble out with the fæces, or may pass by a retrograde course into the bladder; but, in either case, it is expelled per cloacam not per urethram: the penis in the male subserving the conveyance of the semen only. In all other mammals both urine and semen are carried out by the urethral canal in the male; and, in some Insectivora (Shrews, Moles) and Quadrumana (Slow Lemurs), the clitoris in the female is similarly traversed by a canal, which here, however, is exclusively for the urine. The vaginal orifice intervenes between the prominent and perforate clitoris, figs. 485, 546, c, and the anus.

Clitoris, vagina and vent, Shrew.

[blocks in formation]
« НазадПродовжити »