We rank with the above anomalies a process which, although it does not originally exhibit a diseased textural condition of the arterial coats, at all events results in such, and moreover stands in a near relation to chronic inflammation of the cellular sheath of the artery, the latter being either associated with it, or in rarer instances the indirect cause of its origin, in consequence of previous dilatation of the vessel. It further constitutes the basis of aneurismal formations and of numerous spontaneous obliterations. It is the most frequent form of disease affecting the arteries, and is on that account of the greatest importance. It consists in an excessive formation and deposition of the lining mem-brane of the artery derived from the mass of the blood, and at the same time constitutes hypertrophy of this membrane. - We purpose devoting the following remarks to the consideration of this subject, in which we will endeavor briefly to notice all its most important bearings.

In a highly developed form of this affection, we find the inner surface of a large artery, as the aorta, covered with a foreign substance spread over it at separate points, or in large patches, and forming a stratum varying in thickness, by which the inner surface of the vessel is commonly rendered uneven. This substance is in some places either grayish, grayish-white, faded, and translucent, or in others milky-white, opaque and similar to coagulated albumen; in some rare instances it is colored by the imbibition of haematin over various extents of surface. Its free surface is at the same time smooth and shining, or dull and as it were wrinkled. It is soft, moist, and succulent in the translucent parts, and dense, dry, tough, and elastic in the more opaque portions, resembling a cartilage or fibro-cartilage, with which it is usually compared, and for which it is still occasionally mistaken. In the latter condition it adheres internally to the circular fibrous coat.

This substance admits of being split into lamellae, and drawn away in the form of strata. If this is done at those spots where the deposition forms isolated plates or islands, we discover that one or more of the lamellae thus drawn away, generally the innermost (superficial) ones, terminate beyond the limits of the plates in a delicate membrane, which is prolonged to the contiguous, and apparently normal lining membrane of the vessel.

The thickness and extent of this deposition correspond to the degree of the anomalous condition. It varies in thickness from a quarter of a line to two lines and upwards; and extends in extreme cases over the whole trunk and main branches of the aorta, implicating the entire arterial system.

The deposition is generally the thickest directly over the division of a trunk, or at the bifurcation of a vessel. At these points the deposit is frequently so thick, that the mouths of the divergent vessels are much contracted, and even wholly closed. - The spot at the trunk of the aorta, which next to those we have already mentioned, deserves a special reference as a common locality for this deposition, is the lower wall of the aortic arch adjoining the left bronchus. This deposition, which is in itself highly interesting, is rendered still more so when it undergoes ossification. For as we shall have occasion to show, the osseous concretion gives rise here to an angular curvature, and a consequent contraction of the tube of the aorta.

We find on close examination of the deposit, that it has nothing in common with cartilage or fibro-cartilage, with which it is ordinarily compared and even confounded (cartilaginescence of the arteries), and that it actually consists of structures analogous to the layers which constitute the lining membrane of the vessel (the epithelium, fenestrated membrane, and longitudinal fibrous coat).

The circular fibrous coat is found, when compared with the other arterial coats, to be soft, brittle, cleft, and of a faded, dirty brownish color. The cellular sheath exhibits considerable vascularity and puffiness, or is in a state of sclerosis.

It will be seen from this description of the appearances observed in the more highly developed stages of the disease, that our attention should, on the one hand, be directed to its incipient stages, and on the other to its further progress.

At its commencement, this deposition cannot be detected without a previous familiarity with its appearance. It is then a delicate, soft, succulent membrane, exhibiting a vitreous transparency, and appears in some cases, where it is thrown into small folds by the preponderating contraction of the circular fibrous coat, to be exceedingly thin, and covered with white dots or stripes. The circular fibrous coat is normal, when not altered in consequence of pre-existing inflammation of the cellular sheath.

The deposition continuously increases in thickness by the addition of new strata, and thus gradually passes from the condition of transparency and succulence, characteristic of recent formations, to that state in which it appears opaque, resembling coagulated albumen, and finally presents a ligamentous appearance, having a dull, wrinkled surface.

Before we enter upon the consideration of the metamorphoses which further occur in this deposit, it will be necessary to direct attention to some points which, although of extraordinary interest, have hitherto been wholly overlooked.

On attentively examining the inner surface of a highly diseased artery, we perceive that the deposit is interspersed with openings or foramina, varying in size from a pin's head to that of a poppy-seed. These openings occasionally attract attention by a small drop of blood oozing from them on pressure. In some cases these openings are very numerous, whilst in others it is difficult to detect them. They might, at first sight, be mistaken for the contracted mouths of vessels; but the error of this view is readily made apparent by a closer examination, and by the circumstance that they occur at spots where no such vessels are given off, as, for instance, on the ascending arch of the aorta.

These openings lead to canals, which penetrate to various depths in the deposit, where they either terminate without changing their form, or again divide, and turning, with their branches, in an oblique direction, enter the circular fibrous coat, where they finally ramify. They constitute a system of canals to convey the blood into the deposit and the cleft circular fibrous membrane, which is filled by the blood of the dis eased vesel, and may frequently be seen through the deposit.

As far as we are aware, these canals are not connected with the vascular system of the cellular coat, and do not anastomose with its vessels, although they penetrate as far as its elastic layer.

The manner in which these openings and canals originate is a question of the greatest interest. They are undoubtedly the result of partial resorption in the deposit, by means of which openings are formed, which enlarge into canals by coming in contact with each other in the different strata of the deposit. Their mode of origin is very probably similar to that of the apertures Of the fenestrated or striated arterial coat, and is closely connected with it; it is very likely, also, the same process which Stilling observed in the thrombus of tied arteries, and which we have also noticed in a fibrinous coagulum in the heart (in the so-called polypus of the heart), where it rendered the coagula porous, and caused them to acquire a cavernous structure, erroneously regarded as a condition of vascularity.

This channelling of the deposit undoubtedly constitutes the basis of that degeneration of the arterial walls which Lobstein considers under the head of softening of the arteries (arte'rio-malacie). The wall of the artery, in some few cases, degenerates into a spongy tissue, resembling the corpus cavernosum, or occasionally into the form of a tumor, from which, when it is cut, blood pours forth from an innumerable quantity of openings, as from a sponge.

The metamorphoses through which the above described deposit passes, after it has become completely opaque, are the so-called atheromatous process, and ossification of the arteries..