Which of the following develops from the third pharyngeal pouch?
Ans. b (Inferior parathyroids). (Ref. Human Embryology by JB singh, 7th ed., p 112)Branchial (Pharyngeal) pouch derivatives include:First pouch derivatives--middle ear cavity, Eustachian tube, mastoid air cells.Second pouch derivatives--epithelial lining of palatine tonsil.Third pouch (dorsal wings)--inferior parathyroidsThird pouch (ventral wings)--thymusFourth pouch derivatives--superior parathyroids.Also remember:Branchial/ pharyngeal apparatus: Consist of1. Branchial clefts (derived from ectoderm)2. Branchial arches (derived from mesoderm and neural crests)3. Branchial pouches (derived from endoderm).BRANCHIAL ARCHESFirst arch derivatives# Meckel's cartilage: Mandible, malleus, incus, sphenomandibular ligament.# Muscles: Muscles of mastication (temporalis, masseter, lateral and medial pterygoids), Tensor Tympani, Tensor veli Palatini, Mylohyoid, Anterior-belly of digastric.# Nerve of first arch: Mandibular nerve (post-trematic) and chorda tympani (pretrematic).Second arch derivatives# Reichert's cartilage: Stapes, Styloid, Smaller (lesser) horn & superior half of hyoid, Stylohyoid ligament (Hint--4'S').# Muscles: muscles of facial expression, Stapedius, Stylohyoid, posterior belly of digastric.Third arch derivatives# Cartilage. Greater horn of hyoid, lower half of hyoid.# Muscle: Stylopharyngeus# Nerve of third arch: Glossopharyngeal nerve.Fourth arch derivatives# Cartilages: thyroid, cricoid, arvtenoids, corniculate, cuneiform.# Muscles : Most pharyngeal constrictors, circothyroid, and levator veli palatini.# Nerve of Fourth arch: Superior laryngeal branch of vagus nerve. Fifth arch# Fifth arch Makes no major development contributions.Sixth arch derivatives# Muscles: all intrinsic muscles of larynx except cricothyroid.# Nerve of sixth arch: Recurrent laryngeal branch of vagus nerve.BRANCHIAL CLEFT DERIVATIVES# First cleft develops into external auditory meatus# Second to Fourth clefts form temporary cervical sinuses, which are obliterated by proliferation of second arch mesenchyme.# Persistent cervical sinus can lead to a branchial cyst in the neck.Educational points:Treacher Collins syndrome is first arch syndrome - mandibulofacial dysplasia - caused by autosomal dominant gene - resulting in malar hypoplasia with down-slanting palpebral fissures - defects in the lower eyelids - deformed external ears- and sometimes abnormalities of the middle and internal ears.Third and fourth pouch syndrome or DiGeorge' syndrome or CATCH syndrome:# Cleft palate,# Abnormal facies# Thymic aplasia T cell deficiency# Ca++ deficiency &# Heart defects
Superior parathyroids
Inferior parathyroids
Tonsils
Thyroid gland
Pharyngeal Arches