abnormal pharyngeal pouch morphology abnormal first pharyngeal pouch morphology MP:0013222 MPheno.ontology abnormal 1st branchial pouch morphology abnormal 1st pharyngeal pouch morphology abnormal first branchial pouch morphology any structural anomaly of the first endodermal branchial pouch located between the first and second branchial arches; in mammals, the first pouch elongates to form a diverticulum known as the tubotympanic recess; the distal portion of this recess expands to reach the first branchial groove and form the middle ear cavity (aka tympanic cavity) and mastoid antrum; its proximal part remains tubular and forms the auditory tube (aka Eustachian or pharyngotympanic tube), which forms a communication between the nasopharynx and tympanic cavity