On the Significance of the Neuromeres and Similar Structures in Vertebrate Embryos
About the time of closure of the neural folds, transverse bulges—so-called proneuromeres (Källén & Lindskog, 1953)—appear in the wall of the central nervous system of vertebrate embryos. They are very similar to the well-known neuromeres, but are relatively larger and therefore fewer in number. The first proneuromeres to develop are the rostralmost ones and the others develop in a rostro-caudal sequence. They start to disappear simultaneously at two places: the caudal end of the spinal cord and a short-distance caudal to the otic vesicle. When the proneuromeres have disappeared in the spinal cord and the caudal part of the brain but are still left most rostrally, the neuromeric bulges develop. The neuromeres have been described many times in the previous literature (see Bergquist's survey, 1952b). They develop and disappear in a similar way to the proneuromeres (Bergquist, 1952a; Källén & Lindskog, 1953). While the neuromeres are disappearing a third system develops: the migration areas.