A very few of these forms occur in the vascular system generally, and especially in the arteries.

1. Among the productions of fibroid tissue we may include sclerosis of the cellular sheath in consequence of its chronic inflammation, and perhaps also that metamorphosis of the deposit in which it becomes converted, in many cases, into such a tissue:

2. An anomalous production of bone occurs in the following forms: a. The well-known ossification of the arteries - a metamorphosis of the deposit - to which we have already sufficiently alluded. The frequency of its occurrence in the different portions of the system, corresponds with that of the morbid deposition in the arteries on which it depends. A similar relation exists in reference to the periods of life and the sex in which it most frequently occurs.

b. Chalky, mortar-like concretions, formed by the thickening of the atheromatous mass, or by the metamorphoses of the fibrinous vegetations deposited on the above-named bony plates, etc.

c. Ossification of the occluding plug, which owes its origin to inflammation with exudation on the inner coat of the vessel, after the previous conversion of the plug into a fibroid string.

3. The numerous forms in which the anomalous 'production of fat occurs are extremely important. The cholesterin which is contained in the so-called atheroma of the arteries, is the only fatty product that has been hitherto noticed (Gluge, Gulliver). Yet the fatty degeneration of the circular fibrous coat (see p. 203), which may be compared to steatosis of the muscles, is, in our opinion, more important in its results, whilst the excessive formation of fat that is combined with ossification of the arteries, present numerous points of interest, both on its own account and in consequence of. many analogous conditions (see p. 206).

4. Cysts are of very rare occurrence in the arteries, and probably only appear in the cellular sheath and the neighboring tissue. We have never yet observed a case of this nature. Corvisart attempted to build up a theory of the formation of aneurism on two cases which he had observed, but his views were long since refuted, and never met with support.

5. Tuberculosis neither occurs here nor in any part of the vascular system. The deposit does indeed, as we saw at p. 206, give indications of an analogous process, which gives interest to the fact that this disease does not occur in the venous system as a constitutional one.

6. The larger arteries with thick walls steadily resist the invasion of Cancerous Degeneration, and in this respect present a striking contrast to the veins. Whilst the veins traversing a cancerous tumor exhibit cancerous degeneration of their walls, and are often completely filled up by cancerous excrescences, the arteries are found to be undestroyed. While the spontaneous coagulation of the blood in the arteries is rare, we find that the tissue developed from it is still more rarely of a cancerous nature. Yelpeau and others have observed the very rare occurrence of an obstruction of the aorta and iliac arteries by a plug of a cancerous nature, in an individual exhibiting a general cancerous dys-crasia. The rarity of cancer of this form - primary cancer of the arteries - is worthy of notice, when contrasted with its more frequent occurrence in the veins.