abnormal axial mesoderm increased axial mesoderm size 2013-11-14T11:49:43Z MP:0012274 MPheno.ontology csmith expanded axial mesoderm greater than average size 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