BIO Lecture Notes - Lecture 1: Glossopharyngeal Nerve, Maxillary Artery, Ductus Arteriosus
20 Oct 2022
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Document Summary
The development of the head and neck begins in the 4th and 5th week. Growth of mesenchymal tissue (connective tissue) in the cranial region of the embryo results in the formation of arches, separated by clefts. These are the pharyngeal arches and pharyngeal clefts. Simultaneously, a number of outpocketings appear on the lateral wall of the pharynx. The pouches separate the arches on the internal (endodermal) surface whilst the clefts separate the arches on the external (ectodermal) surface. In this article, we will explore these structures from outside to inside and discuss the structures that arise from the pharyngeal apparatus. However, only the 1st cleft gives rise to a permanent structure in the adult the external auditory meatus. The 2nd, 3rd and 4th clefts only form temporary cervical sinuses which are then obliterated by the rapidly proliferating 2nd pharyngeal arch. There are six pharyngeal arches however, the 5th regresses soon after forming.
