Ossification is the second form of metamorphosis of the deposit. This includes the well-known ossification of the arteries. It presents many essential points in common with the atheromatous process, and occurs only in a deposit of comparatively extensive thickness, beginning in the lowest strata, where it is first manifested by the pale turbidity of the deposit, which has then become opaque.

When the process of ossification has been completed, and the metamorphosis has extended throughout the whole thickness of the deposit, the osseous concretion lies exposed. Its form is that of a concavo-convex plate, having a tolerably smooth, even, and concave inner surface, and a rough, nodularly uneven, convex external surface, with irregular and jagged margins. The bony plate is bored through at the point where a branch of the ossified artery is given off, unless the mouth has already been previously closed by the deposit. In arteries of large calibre, as the femoral arteries, the concretions present the form of rings which enclose more or less of the circumference of the vessel.

The number and size of these concretions are subject to great variations; in some cases they only appear at detached points, whilst in others, the artery appears to be converted into a more or less solid osseous tube.

In large arteries, the exposed bony plates are often partially detached by the current of the blood, when they remain in the vessel at different angles of inclination. Their rough margins readily become the seat of fibrinous vegetations.

This form of arterial ossification exhibits a yellow color, and, in general, considerable density and hardness of texture. It is deficient in the delicately lamellated structure of bone, and has no medullswy canals or bone-corpuscles. (See Miescher, Valentin).

The seat of arterial ossification is the lining membrane of the vessel, which is itself produced in anomalous excess. The bony plate does not, according to the general view, remain stationary between the inner and the circular fibrous coat; nor does it press these layers asunder, and induce atrophy in the former of the two by pressure, but it is developed in the parenchyma, and in the numerous thick superimposed strata composing the recently formed inner coat of the vessel. It at length becomes exposed in the artery, in consequence of the final ossification of the innermost lamellae, and not simply from their atrophy.

Besides these, other concretions are occasionally observed in the arteries. Thus, for instance, granular or stalactitic calcareous masses are occasionally found upon the inner surface, or the raised margin of these bony plates. These are either thickened, cretified, atheromatous substances (see p. 202), or cretified fibrinous vegetations.

According to our view, although in opposition to that of many good pathologists, these two processes or metamorphoses very commonly coexist; but, it must be admitted, without any marked preponderance in either of them.

Having given the above description of this deposit and its metamorphoses, and having observed that all the different conditions of this deposition very frequently exist in the same vessel, we purpose, in the following remarks, to consider the relation simultaneously exhibited by the other coats of the arteries.

1. At The Commencement Of The Deposition

At The Commencement Of The Deposition, and till it attains some degree of thickness, there is no perceptible alteration in the circular fibrous coat. But such alterations become the more apparent in proportion to the increasing thickness of the deposit; for this coat gradually acquires a dirty yellowish color, its texture becomes looser, and it admits, with uncommon readiness, of being separated into fibres and layers; at the same time it loses its elasticity, and yields to the pressure of the column of the blood, whence dilatation of the vessel supervenes to a degree that corresponds to the extent of inflammation already set up in its cellular sheath. It loses its power of resistance, and becomes thinner in consequence of this dilatation.

In the more highly developed stages of this deposit, and when the atheromatous and ossifying processes have become fully established, and even made considerable progress, the circular fibrous coat presents a dirty brown, yeast-like color, and is soft, lacerable, and cleft. As the dilatation of the vessel increases, the fibres gradually separate, and the deposit sinks into the interstices thus produced, where it comes in contact and finally coalesces with the cellular sheath, which has in the mean time been converted into a callous tissue.

According to our observations, this disease of the circular fibrous coat depends on the development of fat - fatty degeneration, by which, analogously with the process observed in the so-called fatty metamorphosis of the muscular tissue, its peculiar ramifying fibres and its elasticity are destroyed.

This coat is directly implicated in the atheromatous process, which extends to it from the deposit, and destroys it.