The development of the prechordal plate and mesoderm of amblystoma punctatum

This paper describes the development of the prechordal plate and mesoderm of Amblystoma punctatum from the late yolk‐plug stage to the stage of about nineteen somites. In the earliest stage described the prechordal plate is embedded in the roof of the archenteron and flanked on both sides by prechordal mesoderm with which it is fused. The characteristics and limits of the prechordal plate and mesoderm are discussed and the fate of both traced. It is demonstrated that the mesodermal cores of the mandibular arches are probably largely derived from the prechordal mesoderm which flanks the prechordal plate. The prechordal plate is later separated out of the roof of the foregut in a caudocephalic direction, giving rise to a median mass of mesoderm which expands laterally independently of the mandibular portions of the prechordal mesoderm to give rise to head mesenchyme lying largely anterior to the level of the hyoid arch. The expansion of this mesoderm is followed in some detail. The boundary between prechordal and notochordal regions is placed at approximately the boundary between the mandibular and hyoid arches. The question of the interpretation of the prechordal region is briefly discussed.