_Usual seat of the laceration._ The part of the uterus in which laceration is most frequently observed to occur is near to or at the junction of the uterus with the vagina: this happens rather more frequently behind than before, but the difference in this respect is very trifling. Thus in 36 cases which were collected by Mr. Roberton, of Manchester, "in 1 the cervix was separated from the vagina except by a thread: in 11 the laceration was posterior, in 8 it was anterior, in 5 lateral, in 3 anterior-lateral, and in 3 posterior-lateral." (_Edin. Med. and Surg. Journal_, vol. xlii. 1834, p. 60.) In 34 cases which occurred at the Dublin Lying-in Hospital, "in 13 the injury was at the posterior part; in 12 anteriorly; in 2 laterally; in 1 the mouth of the womb was torn, and in 6 the particular seat of the laceration was not described." (_A Practical Treatise on Midwifery_, &c., by Robert Collins, M. D., 1835, p. 244.) The nature and extent of the laceration varies a good deal: in the worst cases the uterus is torn completely through, and the child escapes either partly or wholly into the abdominal cavity; whereas, in many, the peritoneum has not given way, the laceration being confined entirely to the tissue of the uterus itself. Thus, in 9 of the 34 cases recorded by Dr. Collins, "the peritoneal coat of the uterus was uninjured, although the muscular substance of the cervix was extensively ruptured." In other instances the peritoneum has been cracked or torn in numerous places without any injury to the subjacent tissue. From the greater degree of resistance to the passage of the child, in cases of first labour, we might naturally suppose that rupture of the uterus would be more frequently seen among primiparæ: this, however, is not the case, for of 29 cases mentioned by Mr. Roberton, only one of them was a primipara; a larger (and as an average probably more correct) proportion, viz. 7 in 34, has been given by Dr. Collins: of the multiparæ, 5 were in their sixth pregnancy, 2 in their tenth, and 2 also in their eleventh pregnancy. Experience also shows that in a large proportion of these cases, the duration of the labour has been very far from being longer than usual; indeed, in a considerable majority, the mischief has taken place very few hours after the commencement of active labour. Thus, the average duration of it in the 36 cases recorded by Mr. Roberton, was 15 hours: in 24 of those by Dr. Collins, it was 17 hours: but if we take merely the _majority_ of them we shall have a much smaller average: thus, in 20 of Mr. Roberton's cases it was 9 hours, and in 15 of Dr. Collins's it was only 6 hours.