2. The second form of aneurism of the heart is either the remote consequence of the combined inflammation of the endocardium and of a somewhat thick layer of the muscular substance, or more frequently of inflammation of the wall of the heart throughout the whole of its thickness, accompanied with endocarditis and pericarditis. The inflammation of the muscular substance, by its tendency to induration, promotes the developmerit of a white fibroid tissue, which occupies the place of the muscular fibre in the trabecule, as well as in the actual muscular substance of the heart, and coalesces, as it were, on its inner surface, with the endocardium, which is thickened into a similar tissue, and towards the exterior, with cellular or fibroid formations, - the products of endocarditis and pericarditis. This tissue, with its inherent tendency to shrivelling, is unable to resist the pressure and flow of the current of the blood, and by its yielding and expanding gives rise to circumscribed dilatation of the cavity of the heart. The limits of this dilatation generally correspond with those of the metamorphosis of the muscular substance, extending as far as the point where the muscular fibre has remained undestroyed throughout the whole, or a considerable depth, of the thickness of the wall of the heart. The course of the development of this aneurism of the heart is therefore chronic, when considered as a remote result of the above-named combined inflammations.

It follows from the above observations, that this form of aneurism of the heart is a circumscribed dilatation of one of the cavities, whose walls consist wholly or for the most part of a fibroid (tendinous, ligamentous, cellulo-fibrous, callous) tissue. This circumscribed dilatation exhibits a shallow sinus in the muscular wall of the heart, or an ordinary roundish sac, or even a mere appendage to the heart, which communicates with the cavity, by means of an opening, corresponding in size to the cavity itself, or in some cases by a narrow aperture, or even by a short canal. This appendage either rises above the cavity of the heart from a broad basis, or rests upon it by means of a neck-like constriction. The size of the aneurism varies from that of a pea, a bean, or a nut, to that of a hen's-egg, or of the fist, or may be even larger. The form and size of these structures no doubt mainly depend on the extent and depth to which the metamorphosis of the muscular substance affects the walls of the heart, on their duration and locality, on the patency of the openings of the cavity of the heart, and on the original degree of tenseness and capacity for resistance in the walls of the aneurism. It is probable that the size of the aneurism will be the greater, and that it will the more nearly approximate to the form of a true sac or appendage, in proportion to the extent and penetration of the inflammation of the muscular substance, to its duration, its exposure to the action of the blood flowing into the heart and entering its own cavity through the action of the still uninjured muscular substance, to the degree of contraction affecting the openings in the respective cavities of the heart, and to the yielding of the adventitious tissue constituting the walls of the aneurism. Instead of coalescing with the pericardium, as is usually the case, large aneurisms have occasionally been met with, adhering directly to the thoracic wall and the lung.

The walls of this form of aneurism of the heart consist, as has been already remarked, of a fibroid tissue, which having taken the place of the muscular substance, coalesces internally with the thickened endocardium. The walls of this form of aneurism never present the slightest trace of a separation of continuity, either in the endocardium alone, or simultaneously in it and in one of the contiguous layers of the muscular substance; for the thickened investment of the aneurism occupying the place of the endocardium always extends beyond the boundaries of the aneurism to the normal wall of the heart, where it is gradually lost in the normal endocardium. The assumption that there is a Ioesio continui in the endocardium may have originated in the circumstance that the endocardium of the cavity in question is frequently found to be hyper-trophied, that is to say, that it presents several newly-deposited layers, the most recent of which extend to the limits of the aneurism, which is filled with fibrinous coagula. The occurrence of an excessive morbid formation of the endocardium on the lining membrane of the vessels, from the blood, as shown in diseases of the arteries, must necessarily, from its great extent and importance, lead to future investigations. This form of aneurism of the heart corresponds to true aneurism of the arteries.

The walls of these aneurisms vary in thickness, although they are always thinner than the neighboring uninjured wall of the heart. They probably become so attenuated, in proportion to the increasing size of the aneurism, as to appear as if they were merely formed by the contact of the endocardium or pericardium, or of a doubled endocardium, in consequence of the aneurism having been developed towards another cavity of the heart. Osseous concretions, especially in the form of laminae, are frequently developed in the tissue constituting the walls of the sac, whence the aneurism acquires a partially osseous character. (See p. 151).

The cavity in this species of aneurism is very frequently filled with tough stratified fibrinous coagula, as in aneurism of the arteries. This, however, is usually the case only in larger aneurisms, and in fact the mass of fibrinous layers will, in general, be proportional to the size of the aneurism and to the extent to which the muscular fibres are destroyed.

The inner surface of these aneurisms of the heart occasionally exhibit the ordinary villous, shaggy, and warty, or even the so-called globular vegetations.

It is, moreover, worthy of remark, that new layers of endocardium are frequently found to be deposited in great numbers, and to a considerable thickness, upon the inner surface of the aneurism. It is only on a close inspection that they can be detected lying upon the subjacent fibroid tissue. The atheromatous disintegration they occasionally exhibit, imparts a certain degree of importance to their presence, since this atheromatous process is, in some instances, the cause of the origin of aneurism of the heart.