Experiments on the u Overgrowth ' Phenomenon in the Brain of Chick Embryos by HARRY BERGQUIST

PATTEN (1952) described 'a curious distortion of the central nervous system' in human embryos measuring 5,7,12-5,20, and 30 mm. in length, as well as in some pig embryos. The malformation was called'overgrowth of the neural tube'. Instead of the indecisive word 'overgrowth' the present writer suggests the more exact term 'hypermorphosis' should be used for this malformation. Patten described it in the following way: 'the neural tube epithelium had started to grow wildly so that it became folded, and refolded on itself, as if it was crowded into a cranial space fairly normal in size and shape'. The phenomenon was most distinctly developed in the rostral part of the neural tube. In some cases the cranial cavity was expanded by the process, giving rise to a high-crowned skull. In other cases an encephalocoel was formed. In later papers (1953,1957) Patten discussed this phenomenon further. A malformation in the chick brain, similar to that described by Patten, was obtained by Kallen (1955) as the result of operations in the rostral part of the rhombencephalon. Other papers have been published on similar malformations. The literature is reviewed by Kappers (1956, 1957), who described overgrowth in a human embryo 7 weeks of age which had been damaged by a rubeola infection of its mother. The folding process was especially marked in the telencephalon, and similar abnormalities were seen in the dorsal parts of the diencephalon, mesencephalon, and rhombencephalon. The optic vesicles and the ventral parts of the brain were only slightly affected. A cranioschisis and encephaloschisis were present. In the chorioid plexus Kappers described abnormalities consisting of rosette-like cell formations. He is of the opinion that the encephalocoel was secondary to the strongly marked folding of the brain-wall. Van Limborgh (1956) found pronounced overgrowth in the hemispheres, the