abnormal pharyngeal arch development abnormal head mesenchyme morphology abnormal pharyngeal arch mesenchyme morphology 2011-09-13T11:46:26Z MP:0011262 MPheno.ontology abnormal branchial arch mesenchyme morphology any structural anomaly in the primordial embryonic connective tissue associated with the branchial arches, consisting of mesenchymal cells supported in interlaminar jelly, that derive mostly from the mesoderm and contribute to facial and cranial nerve-associated structures csmith