abnormal head mesenchyme morphology absent head mesenchyme MP:0013198 MPheno.ontology absence of the primordial embryonic connective tissue of the developing head, normally consisting of mesenchymal cells supported in interlaminar jelly, that derive mostly from the mesoderm and contribute to head connective tissue, bone and musculature in conjunction with cranial neural crest cells absent cephalic mesenchyme absent cranial mesenchyme