The mesenchyma stems from a central accumulation of paraxial mesoderm that comes from the four unsegmented occipital somitomeres. These are the uppermost somites that form post-otic. Later, material of the neural ridge and the epipharynx disk also gets into the pharyngeal arches. From this the skeletal portion as well as the musculature of the pharynx and the face derives. The innervation, though, still indicates the occipital origin of the mesenchyma in that the associated pharyngeal arches are innervated by nerves from the uppermost 4 occipital (post-otic) myotome, i.e., from brain nerves. In contrast to the innervation of the extremities, the nerves are already present before the formation of the muscles.