To this class belong: a. Obliteration of the mouths of a vessel, occasioned by the excessive formation of a tissue, analogous to the lining membrane, within a trunk. - This condition, which is followed by atrophy of the vessel itself, is a mode of obliteration of the arteries which has not been much regarded, and one whose nature is not known. It is the result of the excessive process of deposition in one of the trunks of the vessel, and in the vicinity of the mouth as has already been described at p. 199. The mouth continues to become narrower, until it is finally closed by the last layer deposited around it, whilst it diminishes by the fusion of the mass around the circumference. After this the mouth very frequently appears as if it were closed by a membrane stretched across it. When the vessel has become shrivelled and wasted, the closed mouth presents a cicatrix-like puckered appearance, or has wholly disappeared. Above the closed mouth, the blood carried by the collateral circulation into the vessel coagulates over various extents of surface, until its coagulation is prevented by the circulation established by an anastomosing process. The artery shrivels and becomes atrophied above this clot or plug.

As this process of deposition must be very highly developed in order to produce such occlusions, and as it results in dilatation of the diseased artery, we are able to explain the appearance of these contractions and final obliterations of the mouths of the vessels, more especially upon the branches going off from aneurismal vessels. (See p. 215.) We have already alluded generally to the importance of this obliteration, which is, indeed, self-evident; but it exhibits special interest in some individual cases, among which we may notice the following:

1. The contractions and obliterations of the branches of vessels passing from the arch of the aorta.

2. The contractions and obliterations of the coronary arteries of the heart.

Neither of these is by any means a phenomenon of rare occurrence.

b. The contraction and final impermeability of an artery in consequence of excessive deposition - of its ossification - or of the deposition of fibrinous vegetations on the rough inner surface of the vessel, and their cretefaction. - This may be especially observed where the process of ossification is much diffused on the smaller branches of the femoral arteries; many cases of senile gangrene are based on this impermeability of the arteries, which, however, is seldom observed in vessels of considerable calibre.