_Hydrocephalus._ In many cases it produces much less resistance than might be expected from the size of the head; this is, in great measure, owing to the unusual width of the sutures and fontanelles, but chiefly to the almost entire want of ossification in the cranial parietes, which are little else than membranous, and so flexible as to allow the head to be squeezed into almost any shape. In some very rare cases the head has burst, a large quantity of fluid has come away suddenly, and this has been followed almost immediately by the birth of the child:[115] but in the majority the labour has been tedious and severe, and in some instances attended with dangerous results to the patient; thus, Dr. Merriman has "known one hydrocephalic foetus pass entire, the circumference of whose head was 17 inches; another passed alive and lived nearly an hour, whose head measured in circumference nearly 22 inches; both the above labours were long and painful." Perfect relates a case of hydrocephalic head, of which he has given engraved delineations; the labour was attended with extreme difficulty, and the woman expired in less than two hours after delivery; the circumference of this head was 24 inches. (_Cases in Midwifery_, vol. ii. p. 525.) An interesting case of hydrocephalus, attended with convulsions and laceration of the vagina, has been recorded by Dr. Collins: "the perforator was used, upon the introduction of which into the head fully three half pints of water gushed out; the bones then collapsed, and the delivery was easily completed." (_Practical Observations_, p. 205.) _Cerebral tumours._ The bulk of the head is sometimes increased by tumours or sacs of fluid, which arise from a suture or fontanelle: they are of the same nature as the spina bifida, being formed by a protrusion of the integuments and cerebral membranes from an accumulation of fluid beneath: these are of very rare occurrence, and appear to have retarded labour but little, even although of considerable size. The largest cases on record are those which have been described by Ruysch, where one was as big as the head itself, and another where it was nearly as large as the child's body.[116] A case of fluctuating tumour upon a child's head has been described by Mauriceau, (Case 544,) but the precise nature of it is not very apparent.