abnormal axial mesoderm decreased axial mesoderm size MP:0012272 2013-11-14T11:49:43Z reduced axial mesoderm size deficient axial mesoderm csmith reduced size or deficiency of the part of the middle of the three primary germ layers of the embryo which includes the prechordal mesoderm and the chordamesoderm and gives rise to the prechordal plate and to the notochord MPheno.ontology