Studies of neural tube development in the chicken embryo tail.

The tail regions of chick embryos between stages 21 to 46 were studied by light microscopy using paraffin- and epoxyembedded serial sections. The embryonic tail attains its maximum length at about stage 22. The present study examined the morphogenesis of the caudal neural tube during the reduction and remodelling processes of the embryonic tail. Between stages 21 and 28, the embryonic tail became markedly shorter, and the neural tube, with a single central canal, merged caudally with the short medullary cord and tail bud. Between stages 29 and 31, the neural tube elongated and curved rostrally, while the caudal end of the notochord and the tail bud disappeared. Between stages 32 and 39, after showing various structural changes such as dilatation or rupture and abnormal elongation of its marginal zone the neural tube became shorter. By stage 40, development of the caudal neural tube was essentially complete and the neural tube was shorter than the notochord. The neural tube opened dorsally, as in the adult chicken. The caudal opening may be newly-formed as the open portion was found to contain numerous macrophages.