78 Steps Health Journal

First Pharyngeal Pouch

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The first pharyngeal pouch forms a stalklike diverticulum, the tubotympanic recess, which comes in contact with the epithelial lining of the first pharyngeal cleft, the future external auditory meatus (Fig. 15.10). The distal portion of

Mandibular process

Pharyngeal clefts

Mandibular process

Pharyngeal clefts

Parathyroid gland (inferior)

Parathyroid gland (superior)

Ultimo-branchial body

Figure 15.10 A. Development of the pharyngeal clefts and pouches. The second arch grows over the third and fourth arches, burying the second, third, and fourth pharyngeal clefts. B. Remnants of the second, third, and fourth pharyngeal clefts form the cervical sinus, which is normally obliterated. Note the structures formed by the various pharyngeal pouches.

Parathyroid gland (inferior)

Parathyroid gland (superior)

Ultimo-branchial body

Figure 15.10 A. Development of the pharyngeal clefts and pouches. The second arch grows over the third and fourth arches, burying the second, third, and fourth pharyngeal clefts. B. Remnants of the second, third, and fourth pharyngeal clefts form the cervical sinus, which is normally obliterated. Note the structures formed by the various pharyngeal pouches.

the diverticulum widens into a saclike structure, the primitive tympanic or middle ear cavity, and the proximal part remains narrow, forming the auditory (eustachian) tube. The lining of the tympanic cavity later aids in formation of the tympanic membrane or eardrum (see Chapter 16).

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