These lacerations are generally transverse, and only rarely take a longitudinal direction.

Lacerations are much more frequent in the ascending aorta, at a short distance above the valves, than in the thoracic aorta.

They generally occur in persons of advanced age.

This form of lacerations belongs to the class which has been repeatedly investigated by English pathologists, who have applied to them the inappropriate designations of dissecting aneurisms, or of anomalous or interstitial aneurisms. These observers have not hitherto given a feasible explanation of this process, and they appear to have overlooked the conditions that induce such diseases of texture.

b. The cases belonging to the second series differ in every respect from those of the first. These are lacerations of an artery exhibiting a profoundly diseased condition of the texture of the whole wall - somewhat in the manner of the so-called dissecting aneurism, that is to say, with detachment of the cellular sheath, but this is here always effected by the violent action of the blood extravasated from the rent, and therefore constitutes a secondary occurrence.

A cause predisposing to these lacerations is afforded by a high degree of the disease which we have described at p. 199, and to which we have referred as the cause of origin of aneurism. The cellular sheath of the vessel here firmly coalesces with the yellow coat of the artery, in consequence of a process of chronic inflammation by which its tissue becomes thickened, callous, and condensed.

The inner coats of the dilated artery are lacerated in consequence of their morbid brittleness within the closely adhering, thickened, callous, resistant, cellular sheath, which is here violently detached by the blood, but never over an extended surface, as in the cases belonging to the first series.

The cases belonging to this class are generally longitudinal lacerations, in which the fibres of the yellow coat of the artery are actually torn asunder. Transverse lacerations occur only as exceptions to the rule. When laceration takes place after a very considerable degeneration, with unequal disease of the arterial coats, the rents are irregular and curved. The following case may serve as an illustration of these appearances.

On the 6th of March, 1834, a post-mortem examination was made of the body of a woman, aged 50 years, who had died suddenly two nights before. The autopsy showed the body to be robust, and in tolerably good condition. Both arms bore marks of repeated venesection.

There was a grayish white foam, collected in the trachea.

The lungs were of a dark-red color, very full of blood, and oedematous, excepting in the right lower lobe.

There were two pounds of coagulated and fluid blood in the pericardium. The heart was half as large again as usual, fat, and flabby in the left ventricle, and the Conus arteriosus of the right ventricle was dilated. The auricles and trunks of the vessels contained coagulated and fluid blood.

The ascending aorta and its arch were considerably dilated; their inner surface was uneven, and covered at some parts with a white, opaque, cartilaginous, and smooth deposit, and at other parts with a light-colored, wrinkled deposit of considerable thickness; the mouths of the three branches of the arch of the aorta were contracted. About an inch and a half above the semilunar valves on the concave wall of the ascending aorta there was a jagged, rectangular rent in the diseased inner and middle (yellow) coats of the artery. The longest direction of the rent measured one inch and five lines, and ascended into the arch of the aorta, while its other side (which was only half the length of the former) extended along the posterior wall of the aorta. A rectangular lobule, composed of a portion of the inner and of half the thickness of the middle coat, had been exfoliated from the above-described right angle, and from this point the ascending aorta had lost the cellular sheath, together with the external layer of the middle coat, except at a mere narrow strip on its concave surface. The space between these two laminae was filled with coagulated blood. The external lamina had burst into the pericardial cavity backwards, behind the descending Vena cava, longitudinally and downwards, over a surface extending more than half an inch, together with the contiguous lamina of the pericardium.

The cellular sheath of the aorta was unusually thick, although at the same time of a callous condensation, and intimately connected with the yellow coat. It was of unusual thickness, nearly 1 "' at the arteria inno-minata, and more especially at the right subclavian, and was converted into a whitish, very dense and tough, lardaceo-fibrous stratum, and fused as it were into the yellow coat. It was less thick at the left carotid and the subclavian, although it presented a similar character.

On examining the abdominal cavity, the gall-bladder was found to contain a concretion, about the size of a nutmeg; and the fundus uteri was filled with a fibroid growth, equal in size to a child's head, and attached by a thick pedicle.

These Lacerations, like the diseases in which they originate, generally occur in advanced periods of life. They also usually affect the ascending aorta, which may be explained by the circumstance, that this vessel is, in most cases, especially diseased, while it is at the same time exposed to the force of the blood-wave propelled from the heart.

The heart, as may be conjectured from the observations already made, is subject, in these cases, to dilatation and hypertrophy, more especially of the left ventricle.

Among the aneurismal forms, especially allied to these cases of the second class, we must reckon lacerations of the smaller, diseased arteries, having rigid membranes and having become brittle, which are either frequently spontaneous, or the result of wholly inexplicable conditions, such for instance as we especially see in apoplexy (cerebral hemorrhage).

3. Finally, this laceration may depend upon the removal of the supports of an artery, in consequence of an ulcerous process, and upon a loosening and softening of its texture, arising from its coats becoming infiltrated with the ulcerous secretion surrounding them. This form of laceration more particularly affects delicately constructed arteries of inferior calibre, as, for instance, the branches of the pulmonary artery in the walls of tuberculous pulmonary caverns. In some few cases the laceration is preceded by a lateral (aneurismal) enlargement of the vessel towards the cavern (see p. 198).