Most of the muscles of the head are derived from the mesenchyme of the pharyngeal arches. Myoblasts derived from the mesenchyme of the five pharyngeal arches migrate to form muscles of mastication, muscles of facial expression, and muscles of the pharynx and larynx. These muscles are innervated by the pharyngeal arch nerves. For further detail on this topic see chapter 10.
The muscles of tongue are thought to be derived from the myo-tomes of occipital somites. The myoblasts derived from these myotomes
migrate inferiorly and anteriorly to form the extrinsic and intrinsic muscles of the tongue. Innervation of the tongue muscles by the 12th cranial (hypoglossal) nerve is a clue to the origin of these muscles from the occipital myotomes, because this nerve develops in relation to the occipital feomites.
The extrinsic muscles of the eyeball develop from three masses of condensed mesenchyme, which are located over each optic cup. These masses are derived from mesenchyme that is formed in relation to the prechordal plate. These mesenchymal condensations differentiate into three muscular masses from which various extraocular muscles develop. These muscles are supplied by the 3rd, 4th, and 6th cranial nerves. A study of the comparative embryology reveals that lower fishes and reptiles have three specializd myotomes, called pre-otic myotomes (because they are located rostral to the otocyst) which give rise to the extrinsi'c ocular muscles of eyeball in these animals. The three muscular masses developing around the optic cup in humans are also called preotic myotomes because they are regarded to be homologous to the preotic myotomes of the lower species.