Genes with elevated expression in the mandibular arch were identified by comparing its microarray defined gene expression profile with those of all other E9.5 compartments examined, excepting the maxillary arch. As shown, genes with elevated expression in the mandibular arch are, with rare exception, also elevated in expression in the maxillary arch. It is interesting to note that the cranial mesenchyme, mandibular arch and maxillary arch are all composed primarily of neural crest cells. Ep Ect; epidermal ectoderm, including olfactory placode. Affymetrix Gene 1.0 ST microarray data.