remain standing for twelve or more hours at the machines: the physical powers are unequal to the endurance of so much unceasing labour, the skeleton of the child soon suffers in its growth, and the pelvis almost certainly becomes contracted. Similar effects may also be produced by undue pressure on the other parts of the pelvis. Thus the outlet may become much contracted by sitting many hours a day on a hard seat, as is frequently the case in schools. The tubera ischii are pressed together, the pubic arch is thereby contracted, and the sacrum becomes strongly curved forwards. Much riding on horseback at an early age is said to be injurious; and it is stated that the females of those American nations who are constantly on horseback bear but few children, and are frequently three or four days in severe labour. _Rickets._ Similar effects, only in a much more aggravated form, are produced by rickets in early life; the pelvic bones having become soft from the loss of their earthy matter, gradually give way under the pressure of the superincumbent trunk, to the support of which they were unequal. In this way the sacrum is forced downwards and forwards towards the symphysis pubis, the acetabula are driven upwards and backwards, the pubic arch becomes distorted; and if the disease continues for a considerable period of time, the whole pelvis becomes so squeezed together as entirely to lose its original proportions. The manner in which the distortion takes place varies exceedingly, and will be more or less influenced by the circumstances under which the child has been placed. The most constant change is the shortening of the antero-posterior diameter at the brim. In severe cases the base of the sacrum has, as it were, sunk down between the illia, so that its promontory occupies the cavity of the pelvis, the fourth, or third, or even the second, lumbar vertebræ occupying its former position. The gradual yielding of the bones seldom takes place with that degree of uniformity as to allow the sacrum to approach the symphysis pubis in a straight line: the more common result of rickets is, that the promontory is, at the same time, wrung more or less to one side.