Numerous lymphatics pass from the spleen through lymphatic glands, lying near the splenic artery. This or gan is supplied with nerves by branches from the great sympathetics and par vagum, which form a plexus round the great vessels. No excretory duct has been discovered belonging to the spleen.
The uses of the spleen in the animal economy are not completely ascertained ; and we shall not, in this place, even enumerate the various hypotheses that have been contrived to account for the presence of an organ so large, and so well supplied with blood. The late ex periments of Mr Home appear to prove, that at least one important use of the spleen is to convey front the stomach to the bladder, by a shorter passage than could otherwise be afforded, that part of the fluids received into the stomach, which is not required for the process of digestion.
The morbid appearances of the spleen do not ma terially differ from those observed in the liver. As in this organ, both the peripheral membrane, and the sub stance of the spleen, have been found in a state of in flammation ; cartilaginous spots have been seen on the surface ; tubercles, or stony concretions, or hydatids, have been discovered within its substance ; the whole organ has heen found very hard, and sometimes much enkrged. The spleen has also been found ruptured, cold row and then this organ has been altogether wanting.
4. Of the Urinary OTans.
The kidneys are situated about the middle of the. dorsal part 01 the bel,y, one on each side the spine, itt the rightt and left lumbar regions. They are placed vcrt.cally, bchiod the intestines, and in' such a manner, that tile atlantal extremity of the right kidney lies im mediately below the tight lobe of the liver, while the atlantal extremity of the left kidney is neatly contiguous to the sacral extremity of the spleen. The right kidney is commonly a little lower than the left. (See Plate XIX. Fig. 10,1. I.) To describe the form of organs, which furnish one of the most familiar comparisons in discriminating the figure of other objects, would be im pertinent; we shall remark only, that their atlantal ex tremities are larger than their sacral ; that their convex margin looks towards the sides of the belly, while the concave depression points mcsiad to the large blood ves sels. They are of a much firmer consistence than either the liver or the spleen, and of a pale red colour. They arc not inveloped in a peritoneal coat, like the other abdominal organs which we have been describ ing, but are surrounded by a considerable quantity of loose, fatty, cellular substance. From this cellular sub
stance is partly derived the proper peripheral membrane that invests the body of the kidney, adhering very closely to it, and being reflected front the concave de pression on its menial margin, over the trunks of the blood-vessels that enter and pass out at this part. This peripheral coat is of a whitish colour, semi-transparent, and allied to the fibrous membranes.
The glandular substance of the kidney consists of two parts, different in their structure and consistence ; one called the cortical substance, forming the peripheral part of the organ, and another called medullary, composing the centre. The medullary part forms seven, eight, or nine conical divisions, each with a convex base, and having their summits converging towards the concave depres sion of the kidney. These summits end in what are called papillate, which project within a cavity called the pelvis of the kidney. The cortical substance is of a darker colour than the medullary which it surrounds, sending productions between the cones that compose the latter, and giving to the cut substance of the kidney a streaked appearance. What is called the pelvis of the kidney, is properly a membranous cavity, formed by the meeting of short membranous tubes, called in fundibula, which surround the papillary terminations of the medullary part of the kidney.
Each kidney receives from the aorta a considerable artery, which is generally given off in a single trunk, though sometimes there are two or even three trunks. The renal artery enters by the menial depression, and immediately divides into a number of branches, that are ramified through every part of the glandular substance, and sometimes even pierce the peripheral coat to the surrounding cellular membrane. It is remarkable, that those arterial ramifications do not inosculate with each other, though the ramifications of the renal veins have frequent unastomoses. Within the cortical substance of the kidney most of the arterial branches terminate, partly in their corresponding veins, and partly in corpuscles, from which arise what are called urinifcrous tubes. These tubes, at their commencement in the cortical substance, are extremely slender and tortuous, but in crease in size, and run in a straighter direction as they unite in entering the medullary part. Here they gradu ally form the infUndibula, which, joining in three con siderable tubes that again unite, form the pelvis, from which is given off the ureter, or general excretory duct of the kidney.