Upon examining a cross-section of a developing embryo's pharynx, we find that:
- The internal pharynx is lined with endoderm, while the outer surface of the embryo's body is covered with ectoderm. The space between the endoderm and ectoderm is filled with mesoderm. In addition, a large number of neural crest cells migrate to this region.
- The outer indentations are referred to as grooves.
- The inner indentations are known as pouches.
- The protrusions between them are called arches.
The pharyngeal apparatus consists of:
- Pharyngeal pouches lined with endoderm on the inner surface.
- Pharyngeal grooves or clefts lined with ectoderm on the outer surface.
- Pharyngeal arches composed of mesoderm and neuroectoderm.
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🧠 CAP covers outside to inside:
Clefts = ectoderm.
Arches = mesoderm.
Pouches = endoderm.
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👉🏿 We have five pharyngeal arches (1, 2, 3, 4, 6), the fifth pharyngeal arch degenerates during
development, and four pharyngeal pouches and grooves (1, 2, 3, 4).
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