Three stillborn fetuses are reported in which an abdominal wall defect was associated with defects in the urogenital and anal region. Autopsy of these fetuses provided clues indicative of how and where the embryonic development went wrong. The malformation involved a disturbance of the cell deposition process, occurring in the caudal part of the embryo. During the cell deposition process, which takes place in the neural crest and the body wall placode, ectodermal cells are added to the mesodermal compartment of the embryo, thus contributing to the anlagen of several structures, including the ventral body wall. In addition, a change in the shape of the embryo is generated. The sequence of events resulting from a disturbance of the cell deposition process is explained.

SUMMARY A three step method using microwave irradiation enabled microscopic slides of human brain tissue to be obtained within one working day: steps 1 and 2 hardened and solidified brain tissue; step 3 completed formalin fixation. The efficacy and precision ofthe method was compared with slides of conventionally processed brain tissue that had been fixed in formalin for six weeks. The microscopic quality of the sections was excellent with good presentation of brain tissue and equalled that of conventionally processed slides.In many pathology laboratories brains removed at necropsy are suspended in 10% buffered formalin and fixed for at least six weeks. Unfixed brain tissue is soft and delicate, requiring careful handling. The cerebrum is therefore only cut after fixation.1 To shorten fixation time (from six to three weeks) perfusion with formalin is sometimes carried out.2 If, due to time pressure, the brain has to be sectioned before it can be hardened by the fixative, very thick slices must be cut with great care. Even then distortion can hardly be avoided. The thick slices can be fixed in 48 hours provided that the fixative is changed several times. ' Since the early 70s, it has been reported that heat produced in tissues by microwave irradiation can be used for fixation.3 This principle is used in neurochemical and pharmacological research in laboratory animals.6 7 Reported fixation times are in the range of seconds to minutes. Microwave irradiation can be of value in the hardening procedure to permit cutting8 and in the fixation step.9 Moreover, in tissue treated in this way the fixative diffuses more rapidly.' I In this paper we report how this three step action of microwave irradiation can be exploited for use on human brain tissue. Material and methodsFresh human brains from four patients without major cerebral disease, obtained within 12 to 18 hours after death, were used for this study. There were two men Accepted for publication 16 December 1987 and two women ranging in age from 26 to 82 years. Causes of death were cardiac infarct (n = 3) and acute lymphatic leukaemia (n = 1).

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