. A laboratory manual and text-book of embryology. Embryology. 170 THE ENTODERMAL CANAL AND ITS DERIVATIVES pharyngeal pouches soon connect with the pharyngeal cavity through wide open- ings. The third and fourth pouches grow laterad and their diverticula com- municate with the pharynx through narrow ducts in 10 to 12 mm. embryos (Fig. 162). When the cervical sinus is formed the ectoderm of the second, third and fourth branchial clefts is drawn out to produce branchial and cervical ducts and the branchial vesicle. These are fused at the closing plates with the entoderm of the second, third and
. A laboratory manual and text-book of embryology. Embryology. 170 THE ENTODERMAL CANAL AND ITS DERIVATIVES pharyngeal pouches soon connect with the pharyngeal cavity through wide open- ings. The third and fourth pouches grow laterad and their diverticula com- municate with the pharynx through narrow ducts in 10 to 12 mm. embryos (Fig. 162). When the cervical sinus is formed the ectoderm of the second, third and fourth branchial clefts is drawn out to produce branchial and cervical ducts and the branchial vesicle. These are fused at the closing plates with the entoderm of the second, third and fourth pharyngeal pouches. Branchial cleft 1 Cervical sinus Cervical duct Thymus anlaqe Epithelial body of 4n pouch Trachea. Pharyngeal pouch 1 Pharyngeal pouch Z Pharyngeal pouch 3 Pharyngeal pouch 4~ â Apical bud of' riaht Lung Siomach Dorsal 'pancrea Gall bladder Duodenum Fig. 162.âA reconstruction of the pharynx and fore-gut of an mm. embryo seen in dorsal view (after Hammar). The ectodermal structures are stippled. The first and second pouches soon differ from the others in form and give rise to an entirely different type of permanent structures. With the broadening of the pharynx the first two pouches acquire a common opening into it, the primary tympanic cavity. The first pouch later differentiates into the tympanic cavity of the middle ear and into the Eustachian tube. By the growth and lateral expansion of the pharynx the second pouch is taken up into the pharyngeal wall, its dorsal angle alone persisting to be later transformed into the palatine Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Prentiss, Charles William, 1874-1915. Philadelphia, London, W. B. Saunders
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