In this case the labour is rendered difficult or impossible to be completed by the natural powers on account of the faulty size, form, or condition of the child. In the first instance, it is merely a case of disproportion between the child and the passages, owing to the unusual size of the former. Where the child is well formed throughout, but larger than usual, it rarely happens that the head experiences any serious degree of difficulty in passing through a well-formed pelvis, the greatest resistance being observed during the dilatation of the external passages. Even when the head is born, the shoulders may produce a considerable obstruction to its farther passage, requiring a good deal of careful manipulation, in order to disengage the foremost shoulder from under the pubic arch, and thus diminish the pressure of the child against the parietes of the pelvic cavity. Where the shoulders have been severely impacted in this position, it has been in great measure owing to the practitioner having endeavoured to bring down the wrong shoulder first, viz. that which is directed more or less backwards. _Size of the child._ We have already stated that the average weight of the full grown foetus is between six and seven pounds, and its length about eighteen inches; but it is frequently found to exceed these proportions very considerably. Children are not uncommonly observed to weigh 10lbs. at birth. Dr. Merriman once delivered a still-born child, which weighed 14lbs., and the late Sir Richard Crofts is said to have delivered one alive which actually weighed 15lbs.; but by far the largest child which we have yet heard of is recorded by Mr. J. D. Owens, surgeon, at Haymoor near Ludlow; it was born dead, and the weight and admeasurements ten hours after birth were as follow:-- The long diameter from the occiput to the root of the nose 7-1/4 inches. The occipito-mental 8-1/2 From one parietal protuberance to the other 5 Circumference of the skull 15-1/4 Circumference of the thorax over the xiphoid cartilage 14-1/2 Breadth of the shoulders 7-1/4 Extreme length of the child 24 Weight of the child 17 lbs. 12 oz. (_Lancet_, Dec. 22. 1838.)