The mesenchyme for the formation of the head region is derived from mesoderm, neural crest and thickened regions of ectoderm known as ectodermal placodes. The formation of face region is from the contribution of five mesenchymal prominances namely – Frontonasal, two mandibular processes and 2 maxillary processes.
Frontonasal process forms the forehead, the nasal septum, philtrum of upper lip and premaxilla bearing upper four incisor teeth. Maxillary process forms whole of upper lip except the philtrum and most of the hard and soft palate except the part formed by the premaxilla. Mandibular process forms the whole lower lip.
Derivatives of pharyngeal arches
Arch number 1 – Mandibular arch
- Quadrate Meckel’s cartilage.
- Carilagenous derivatives – Incus Malleus Anterior ligament of malleus Spine of sphenoid Sphenomandibular ligament Genial tubercle of mandible.
- Muscles belonging to the arch – Tensor tympani Muscles of mastication Mylohyoid Anterior belly digastric Tensor veli palatine.
- Nerve of the arch – Trigeminal (V) Mandibular division.
- Artery – First aortic arch artery.
Arch number 2 – Hyoid arch
- Reichert’s cartilage.
- Cartilagenous derivatives are – Stapes Styloid process of temporal bone Stylohyoid ligament Lesser horn and upper part of Body of hyoid bone.
- Muscles belonging to the arch are – Stapedius Stylohyoid Facial muscles, incl. Buccinator Platysma Posterior belly digastric.
- Nerve supply is by the facial nerve.
- Artery of the arch is Stapedial.
Arch number 3
- Greater horn and lower part of body of hyoid.
- Stylopharyngeus muscle arises from this arch.
- Nerve of the arch is glossopharyngeal.
- Artery is – Common carotid artery, first part of internal carotid artery.
Arch number 4
- Cartilage derivative – Thyroid cartilage, Cunieform cartilage and Corniculate cartilage.
- Muscles of the arch are – Pharyngeal and extrinsic laryngeal muscles, levator veli palatine.
- Nerve of the arch is vagus.
- Artery – Proximal part of subclavian artery on the right, Arch of aorta between origins of left common carotid and left subclavian arteries.
Arch number 6
- Arytenoid cartilages is the derivative from this arch.
- Muscles of the arch is – Intrinsic laryngeal muscles.
- Nerve – Vagus (X) Recurrent laryngeal branch.
- Artery – Part between the pulmonary trunk and dorsal aorta.
Article by Dr. Siri P. B.
