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or root of the tumour, and the least at its fundus. But observation demonstrates, that, whether the aneurism be recent and small, or of long standing and large, the passage from the artery is always narrow, and the fundus of the aneurism, the farther it is removed from the artery, the more it is enlarged. Another circumstance worthy of attention on this head, which I have likewise pointed out above, is, that the aneurismal sac is always covered by the same soft distendible cellular substance, which in the sound state surrounded the artery, and united it to the adjacent parts; which soft cellular substance, supposing it to be an aneurism of the arch, or of the thoracic trunk of the aorta, is covered by the pleura, and if the aneurism is in the abdomen, by the peritoneum; which membranes include the aneurismal sac, together with the ruptured artery, and present externally, a continued, smooth, shining surface, as if the artery alone was in that way dilated.

"S16. But if, instead of dividing, as is commonly done, the fundus of the aneurismal sac, the aorta be divided lengthwise on the other side, and opposite to the constriction or neck of the tumour, the place of the ulceration, or of the rupture of the proper coats of the artery, immediately appears within the artery, on the side opposite to that where the incision was made, and the fissure which has taken place is immediately discovered, the edge of which is sometimes fringed, often callous and hard, like that of a fistula; through which fissure the arte rial blood had formed itself a passage into the cellular sheath of the artery, afterwards converted into an aneurismal sac. If as sometimes happens in the arch of the aorta in the vicinity of the heart, the artery, before being ruptured, has suffered some degree of enlargement beyond its usual diameter, it appears at first sight that there are two aneurisms; but the constriction or neck which the aneurismal sac next to the artery presents externally, points out exactly the limits, beyond which the internal and muscular coat of the aorta had not been able to resist the distention, and have therefore been torn by it, and shows clearly the difference existing between an aneurism and a simple enlargement in diameter of the tube of the aorta in the vicinity of the heart.

"17. The rupture in the artery is always small in proportion to the large size of the aneurismal tumour; so that when the arch of the aorta has suffered some degree of dilatation before bursting, as sometimes happens near its passage out of the heart, on making an incision on one side into the aneurismal sac, and on the other into the tube of the artery lengthwise,

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two sacs present themselves, separated from each other by means of a partition or diaphragm lacerated in its middle; which partition is formed of nothing else than the remains of the internal and muscular coats of the ruptured artery. And as the limits of the proper coats of the aorta, and the beginning of the cellular aneurismal sac, are marked externally by that kind of constriction or neck which the tumour presents in the vicinity of the artery; in the same manner, internally, this partition, torn in its middle, determines the precise point of the rupture of the proper coats of the artery occupied by aneu rism.

"18. All this acquires a degree of demonstration and certainty, to which nothing can be opposed, by carefully dissecting the proper coats of the ruptured aorta in its situation, and comparing them at the same time with the cellular substance forming the aneurismal sac; for, in the incision made in the direction of the axis of the aorta, and in its side opposite to that where the rupture has taken place, its proper coats are found either perfectly sound, or a little weakened and intermixed with earthy points, but still capable of being separated distinctly into layers from one another; when, on the contrary, in the opposite side of the aorta, where the ulceration or laceration exists, its proper coats are met with unusually thin, blended together, and with difficulty, or in no way capable of being se parated from each other, intermixed very often with heterogeneous substances, which render them brittle like the shell of an egg; and, lastly, disorganized and torn at the place where they form that species of partition, which marks the limits between the ruptured artery and the entrance of the aneurismal sac. Continuing to separate these coats from within outwards, we come to the cellular sheath which surrounds the aorta externally. Then, on removing the cellular pulpy sheath of the aorta, it is found smooth externally, like the artery, villous, cellular, and irregular internally, extending from the circumference of the tube of the artery over the neck and fundus of the aneurismal sac. This external covering or sheath of the artery actually appears, to those who are not sufficiently skilled in such dissections, as if the artery were dilated under it to such a degree as to form the aneurism; and it has still more that appearance if the aneurism is very large and of long standing, since in this case the cellular sheath of the artery becomes unusually thick and pulpy, and because it adheres very firmly to the subjacent muscular coat of the artery at the stricture or neck of the aneurismal sac. But even in these cases, as well as in those of re

cent and small aneurisms of the aorta, by employing care, we may at last succeed in separating, without laceration, this cellular sheath from the tube of the artery, above and below the injury, and successively from the subjacent muscular coat, as far as the neck or root of the aneurism. It is then clearly perceived that the muscular coat of the aorta does not pass beyond the partition which divides its tube from the entrance of the aneurismal sac; and it is distinctly observed, that the fibres and layers of the muscular coat are not prolonged over the aneurismal sac, but terminate like a fringe, or in obtuse points, at the edge of the rupture of the artery. On which account, nothing can be more evident than that the aneurismal sac does not belong at all to the artery, and that, properly speaking, it is only the cellular sheath, which in the sound state covered and connected the artery to the neighbouring parts, which, being elevated by the effused blood, at first in the manner of an ecchymosis, then distended and compressed, has acquired that degree of density, and of additional hardness and thickness, as if it had been formed by the proper coats of the artery, prodigiously relaxed, distended, and thickened. These appearances the more readily lead to error, as both the injured artery and the aneurismial sac, as has been frequently mentioned, are covered by a common smooth membrane externally, such as the pleura in the thorax, and the peritoneum in the abdomen.

"19. The favourers of the contrary opinion do not deny that the artery is sometimes ruptured in internal aneurisms, but they only admit this in those cases in which the dilatation of the artery has been carried to a prodigious extent. The invalidity of this opinion appears to me to be clearly proved by the rupture of the artery being constantly met with, whether the internal aneurism be small or large, and the artery be a little, or, as most frequently happens, not at all dilated. And this opinion is likewise contradicted by its being now ascertained, that the internal and muscular coats of the artery terminate evidently in the fringe, or hard margin of the orifice of the partition, and that the aneurismal sac is not at all formed by the proper coats of the artery, but by the cellular sheath which surrounds it. In the large aneurisms in which the partisans of the common doctrine admit the rupture of the artery, a double rupture is always found, the one of the artery, the other of the aneurismal sac; and this last is that which actually kills the patient, by changing the aneurism from the circumscribed into the diffused state. The erroneous opinion, that the large arteries, and especially the trunk of the aorta, are as it were in

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sulated, or covered only by a very fine membrane, adhering firmly to the subjacent muscular coat, and easily lacerated, has given rise in all probability to the belief, that the ulceration or rupture of the internal proper coats of the aorta could not take place, without this thin tense membrane covering the artery externally being likewise torn. Undoubtedly, if this were the case with regard to the external cellular sheath of the arteries, it would necessarily follow, that the blood should be effused into the thorax and abdomen, in every case of rupture of the abdominal or thoracic aorta. Indeed, we sometimes see this happen in practice, by the combination of some particular circumstances; for, if unfortunately the rupture of the internal and muscular coat of the aorta happens in such a point of the artery, where externally there is only a thin tense membrane closely applied to the aorta, instead of a corresponding soft cellular sheath, we see that this external thin membrane is likewise comprehended in the rupture of the proper coats of the artery, and that therefore sudden death takes place, from the inevitable effusion of blood into some of the principal cavities, especially the thorax. Such is the case whenever the internal and muscular membranes of the aorta are ruptured in that portion of the artery included within the pericardium, which is only covered by a thin reflected layer of it. In this particular circumstance of place and structure, as soon as the proper coats of the aorta are ruptured, this thin membrane is lacerated at the same time, and the blood is immediately effused into the cavity of the pericardium. An example of this kind is related by Walter, and illustrated by a figure; by the Berlin Physicians; and several other fatal accidents similar to these are recorded by Morgagni. I have likewise observed a case similar to the preceding, the history of which I think proper to relate here. Joseph Varani, 22 years of age, a corporal of the 4th company of pioneers, while he was conversing cheerfully with his companions, was struck suddenly dead. This man, formerly by trade a shoemaker, had been repeatedly infected with lues venerea, and had also several times undergone a mercurial course. He had never, however, complained of difficulty of breathing, and his pulse had never been found irregular or intermitting, not even a few weeks before his death. On examining his body, the pericardium immediately presented itself quite distended with blood. The aorta in the vicinity of the heart, at the distance of half an inch above its valves, where it began to be incurvated, presented externally a tumour of the size of a nut, which opened by a small hole within the pericardium.

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The reddish, and, as it were, ecchymosed membrane, of this tumour diminished in thickness in proportion as it approached the place of the rupture, round which it was very thin. On making an incision into the concave part of the aorta, on the side opposite to the seat of the tumour, its internal coat, where it corresponded to the base of the tumour, was quite rough, corroded, interspersed with yellow hard spots, and actually ulcerated for the space of an inch in circumference. In the centre of this ulcerated tract, both the internal and muscular coats of the artery formed a slight pit, into which the point of the fore-finger could be introduced, so that any one, who had contented himself with the appearance of the parts, would have said, that this small tumour, which appeared externally on the beginning of the curvature of the aorta, was formed solely by the weakened and distended proper coats of the artery, or that this tumour was a true aneurism. But on removing carefully from the curvature of the aorta its external cellular sheath, and consequently the reflected lamina of the pericardium, leaving the subjacent fibrous coat untouched, I found that this reddish and ecchymosed sac was formed solely by the cellular sheath, and by the reflected lamina of the pericardium. This cellular capsule, at its base, adhered very firmly to the irregular edges of the ulceration, and rupture of the proper coats of the aorta, in such a manner that the limits of the one and of the other could be clearly distinguished. On which account, in this case there were two ruptures, as in all the others of sudden death caused by aneurism, the one in the proper coats of the artery, the other in its external cellular capsule. The thin, tense, reflected lamina of the pericardium, being provided with very little soft cellular substance under it capable of extension, when raised to the size of a nut, not being disposed to yield any further, burst, and allowed the blood to escape into the cavity of the pericardium. But this is not the case in the other parts of the aorta, in its curvature without the sac of the pericardium, nor in its thoracic and abdominal trunks; through all which tract the cellular sheath of this artery, far from being a fine tense pellicle, adhering firmly to the muscular coat, as within the pericardium, is, on the contrary, a pulpy weak covering, allowing itself to be easily distended. Whence it happens that this cellular sheath is well fitted for yielding to the impulse of the arterial blood which is effused, and, by yielding, it allows

*The pathological preparation mentioned here is preserved in the museum of this university.

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