pharyngeal arch number UBPROP:0000103 gill arch N = PA N-2. the term branchial_arch is ambiguous. pharyngeal_arch_number pharyngeal_arch_number true uberon x pharyngeal_arch_number N if and only if (i) x is a pharyngeal arch, and (ii) x is ancestrally pharyngeal arch number N in a series of pharyngeal arches repeated along a antero-posterior axis, with arch_number 1 being the mandibular arch. anterior_to pharyngeal arch