Amongst the cartilaginous fishes, the supra renal capsules seem in the Squalidm to be only present as a single mass. This, in the shape of a small ochre-yellow stripe, oc cupies the dorsal surface of the kidneys. But in the Rays the supra-renal organs form a curved cylinder, which is constricted at two points, and lies on the ureters ; at least Retzius formerly stated this to be its condi tion. Stannius sometimes found in this genus a similar elongated body behind the kidneys : or, in other instances, Iliar or five small glan dular corpuscles were present in its place. And the latter observer found that the supra renal glands of the Sturgeon* consisted of similar corpuscles in much larger number.
The supra-renal capsules of the cartila ginous fishes have a yellow colour, and are also plainly lobulated.
As has been previously remarked, in the least developed fishes the supra-renal cap sules have not been discovered, at least not with any certainty, so that their existence must remain a matter of doubt. In the Myxinoid fishes, J. Willer -I- found behind the gills, and on each side of the cardia, a clus tered gland which was devoid of an excretory duct. He interprets it as a supra-renal organ; and regards as analogous to it the white specks with which the trunks of the posterior veins of the body are beset in the Ammo cmtes.t But the minute structure of the glands in question in the Myxinoid fishes, which is also described by Miller, seems ra ther to contradict the explanation attempted. And Ecker discovered a gland in the Petro myzon between the aorta and the great vein of the body, and partly lying in the coat of the latter : but this also had not the struc ture of a supra-renal capsule.
II. We next proceed to the minute struc ture of the supra-renal capsules, concerning which Ecker has given a very good and fun damental description, so that we shall here in great degree follow him. In Man and all the Mammalia, they exhibit two kinds of sub stance, which have been designated by the names of cortical and medullary substance. The first is clearer than the latter, being in Man of a yellowish-brown colour ; while the medullary substance possesses a reddish brown hue. In many instances, the two kinds of substance are little distinguishable by the naked eye, so that the supra-renal capsules exhibit only a simple mass, such as Cuvier has described that of the Elephant to be. Besides this, the amount of the two layers varies very considerably. The cortical substance is of some solidity ; while, on the contrary, the medullary matter is very delicate and flaky. This great delicacy, together with its considerable richness in blood-vessels, makes it very probable, that the medullary substance of the supra-renal capsules is de composed very quickly after death. And this gives rise to the formation of a cavity, con taining a brownish-red fluid, which is not un frequently found in the interior of the human supra-renal capsules. Formerly this cavity was regarded as normal and occurring during life. The name " capsulee atrabilarim" is connected with this notion, since these cavi ties were described as real by the older ana tomists. And although decomposition is regarded as the chief agent in the formation of these cavities, yet pathological conditions seem to be by no means without their influence towards them. Thus Rayer tells us the de velopment of cavities may occur in conse quence of rupture of the venous coats, ani the effusion of blood in the medullary sub stance.* Nagel also remarks concerning it, that the suprarenal vein alone, which courses in the centre of the organ, may be instru mental to the production of such a cavity, albeit a small one ; so that by injections through this vein the whole medullary mass may frequently be torn up, and converted into a cavity. The covering of the supra-renal
capsules consists or areolar tissue. At many points of this covering little processes of are olar tissue pass directly into the interior of the medullary substance, and thus separate it into portions or lobes of different form and size. These masses of areolar tissue are finally lost in fine bundles, which separate the elementary parts of the gland from each other. We shall return to this again.
The further composition of the organ which we are now contemplating is better seen in Man than in any others of the Mammalia.
In man the cortical substance appears to be composed of an innumerable quantity of completely shut glandular vesicles, which are united into a mass by the ensheathing coats previously mentioned. At the first glance one might easily imagine that they were not gland-vesicles, but tubes which, lying close to each other, take a radiating course from the centre towards the periphery. It is only at either margin of the cortical substance that the individual small roundish vesicles can be verified. By more careful examination, we can assure ourselves (as was first stated by Ecker) that this tubular appearance is only apparent, and that it is caused by the glan dular vesicles being arranged in rows, so as to cover each other like the tiles of a roof. In this manner the vesicles of a row, especially when they are filled with dark contents, appear like a tube, with a blind termination at each extremity. The observation just mentioned can be best made if the preparation be treated with a dilute solution of an alkali. It will be thus seen that these vesicles of the supra renal capsules are surrounded . by and con structed of a fine, structureless, transparent membrane, to the thickness of which we are unable to assign any measurement, and which, even by the use of the highest magnifying powers of the microscope, appears as only a simple line. This structureless membrane, which modern observers have shown to be a constituent of all glands with the single exception of the liver, we shall indicate by the name of the "nienibrana propria." It is especially distinguished by the fact, that it is not attacked by the dilute alkalies, as caustic potash, and ammonia, but preserves exactly its original appearance ; while the contents of the gland are in general completely dissolved by these agents. The use of these applica tions cannot be too much recommended in examining the glands, as for instance those of the stomach, intestine, &c. —a fact which has been taught me by repeated experiments. The gland-vesicles of the human supra-renal capsules exhibit considerable differences of size; besides which, their form is wont to vary in some degree. The smaller vesicles are roundish, and have a diameter of 8 to 12-1000ths of a line ; the larger of these, which seem elongated, have a length of 18 to 25-1000ths of a line, with a breadth of 10 to 15-1000ths. The smallest of these vesicles occur in the greatest numbers at the limits of the medullary substance ; while, on the con trary, the larger and more elongated vesicles generally occupy its middle. The glandular contents, which are surrounded by the vesicles, appear, by a low magnifying power, as a dense pap-like mass, which seems to be white by reflected, and dark by transmitted light, and consist of granules. Nevertheless on the application of a powerful lens four consti tuents may be distinguished ; namely, — (1) very fine molecules, (2) fatty granules, (3) nuclei, and finally, (I) cells in different stages of their development.