Pharyngeal apparatus

• in 4-5 weeks surface elevations start appearing lateral to developing pharynx. • Initially it consist of core of mesenchyme ( derived from paraxial & lateral plate mesoderm) is covered externally by ectoderm & internally by endoderm. • During 4th week most of mesenchyme is derived from neural crest cells that migrate into pharangeal arches to contribute to skeletal element , while original mesenchyme give rise to musculature & vascular endothelium.

Pharyngeal arches • Six paired swellings -lateral wall of primitive pharynx • Fifth one disappears • Develops in 4th week i.u Components of pharyngeal apparatus • Pharyngeal arches • Pharyngeal clefts • Pharyngeal pouches • Pharyngeal membrane

Components of pharyngeal arch

• Core of mesoderm • Cartilage • Artery • Nerve Derivatives of first arch

• Nerve- Trigeminal nerve • Muscles- muscles of mastication (…), anterior belly of diogastric, mylohyoid, tensor tympani, tensor palati • Cartilage - meckel’s cartilage

ventral (malleus , incus) dorsal (mandible)

• ligaments- sphenomandibular, anterior ligament of malleus Second pharyngeal arch

• All muscles of facial expression • Facial nerve Reicherts cartilage ventral dorsal (lesser cornu stapes upper part of hyoid) • Stylohyoid ligament Derivatives of third arch

• Stylopharyngeus • Glossopharyngeal nerve Cartilage ventral dorsal (disappears) (Greater cornu and lower part of hyoid bone) PLANE OF CUT Derivatives of fourth and sixth arch • Superior laryngeal nerve(4th arch) Vagus • Recurrent laryngeal nerve nerve(6th arch) • 4th and 6th arch cartilage - form cartilage of larynx (thyroid, cricoid, arytenoids and cuneiforms)

• Muscles- cricothyroid, levator palati, constrictors of pharynx, intrinsic muscles of larynx MUSCLES OF BRANCHIAL ARCHES

First - Trigeminal V Fourth Vagus X Sixth Accessory XI Innervated by Derivatives of pharyngeal pouch Derivatives of pharyngeal pouch

• Pouch 1 – Tubotympanic recess - AuditoryTube, Tympanic cavity

• Pouch 2 – lining (crypts of Palatine Tonsils)

• Pouch 3- Inferior Parathyroid Glands & thymus

• Pouch 4 – superior ParathyroidGlands & C-Cells Clinical

• Brachial cyst and fistula- • congenital epithelial cyst • lateral part of the neck • due to failure of obliteration of the second branchial cleft (or failure of fusion of the second and third branchial arches) BRANCHIAL ANOMALIES

• Tracher collin syndrome • Piere robin syndrome • Di- george syndrome