When fine sections of the medullary sub stance of the human supra-renal capsule are examined with the aid of the microscope, it is seen to be considerably clearer and more transparent than the cortical substance ; a circumstance which essentially depends on the fact, that the fatty granules occur more sparingly in the former than in the latter. In Man, and in most of the other Mammalia, it is rendered very distinguishable from the cor tical substance by the absence of the gland vesicles. It is found to consist of a basis of fibrous tissue, which is formed by processes that come off from the sheath of the cortical substance, and in which numerous blood-ves sels and nerves take their course. In the mass of areolar tissue the pulverulent mole cules above described are also met with ; and besides these, nuclei and cells in different stages of development.
Where accessory supra-renal capsules oc cur, they contain, according to Ecker, the same vesicles ; of which the larger occupy the outside, and the smaller the inside. But the two kinds of substance are not present ; the whole tissue answers to the cortical substance of the real supra-renal capsules, and it has a sometimes clearer, sometimes darker, yellowish appearance.
The structure just described obtains with little modification in all the Mammalia. It is true that, at present, only the Carnivora, Ruminantia, Solipeda, and Pachydermata, have been examined. Nevertheless, according to these observations, it is tolerably allowable to generalise concerning all the orders of Mammalia.
In the Ox, the brown cortical substance is divided by strong bundles of areolar tissue into lobules. The gland-vesicles exhibit no thing extraordinary, but, amongst the different constituents of their contents, the fatty gra nules are much more sparingly present than in man. Gerlach* found the glandular vesicles very distinct in the Sheep. The structure of the supra-renal capsules of the Goat and Pig is identical with that seen in the Ox.
In the Horse, the gland-vesicles of the cortical substance altogether correspond with those of the human subject. Here also the smaller and more spherical lie on the ex terior, while the larger and more oval occupy the interior, and offer the tubular disposition already referred to. But their membrana propria is more delicate than in man. In the young Horse the fatty contents of the gland vesicles are in very small quantity; while, on the other hand, in older animals, it predo minates so considerably that it quite conceals all the other contents, and renders their exa mination very difficult.
But the medullary substance in the Horse offers a remarkable distinction from that of the other Mammalia : namely, that it, as well as the cortical substance, contains gland vesicles. These have a variable shape and size;
and are round, oval, elongated, or sometimes curved in the shape of a bow. The contents are the same as usual, only it is much poorer in fat than the cortical substance ; and, on this account, appears much clearer.
The supra-renal capsules of the Rodcntia and Carnivora possess the greatest quantity of fat, and are therefore the most difficult of examination.
Notwithstanding this, the white cortical substance of the Rabbit exhibits the usual ar rangement : and, besides this, the medullary mass not unfrequently presents small circum scribed collections of fat.
Among the beasts of prey, the Deg and Cat have been examined, and in these the nuclei of the contents are with difficulty discover able, owing to the innumerable quantity of the fatty molecules. The nuclei are here also granular in the older, vesicular in the younger animals. A portion of fat not unfrequently surrounds the cells of the glandular contents ; and in this manner large dark globules ori ginate, which completely obscure the enclosed cell. These may especially be seen in the Cat, where they take a clustered arrangement and occupy the limits of the medullary and cor tical substance. The medullary substance is poor in fat. Hitherto the gland-vesicles have not been made out with certainty in this fatty cortical substance, but they are very distinct in the hedgehog.
It yet remains to us to consider the dispo sition of the blood-vessels, lymphatics, and nerves in the supra-renal capsules of the Mamrnalia. For this purpose we shall select those of Man.
Vessels. — In the human subject, each supra-renal capsule is supplied with arterial blood by three trunks :—by an arteria supra rcnalis superior, which is usually present, and comes off as a branch of the phrenica inferior; an arteries supra-renalis media, which is usu ally double on each side, and arises from the aorta ; and finally, an arteria supra-renalis in ferior, which is a branch of the renal artery. The further arrangement of the vascular sys tem has been especially examined by J. Mid ler*, and Nagel t, whose results have been recently confirmed by Ecker. t The numerous small arterial trunks having arrived at the outer surface of the supra-renal capsules, take a different distribution. One part of them immediately pierce the sheath of the organ, and enter its substance; while an other portion of them courses for a consider able distance on the outer surface before be coining lost in the interior.