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Figure 6 | Zoological Letters

Figure 6

From: On the peculiar morphology and development of the hypoglossal, glossopharyngeal and vagus nerves and hypobranchial muscles in the hagfish

Figure 6

Development of hypobranchial muscles. Stage-53 (A–C) and stage-60 (D–F) embryos of Eptatretus burgeri reconstructed to show development of the putative hypobranchial (and abaxial) muscles in the hagfish; left lateral (A), right lateral (D), medial (B, E) and ventral (C, F) views. At stage 53 (A-C), the rostral part of the common anlage for oblique and rectus muscle (m.obl + m.rect) is arising from the ventrolateral edge of myotomes (anlage of parietal muscles, m.par) to grow ventrally into the superficial layer of the hagfish “neck”, appearing as the basal part of the hypoglossal cord in other vertebrate embryos. The epithelial cord (colored blue) indicates the anlage of the mucous gland (mg). At stage 60 (D-F), the parietal and hypobranchial muscles surround the entire pharyngeal basket laterally (E), and only the gill pores penetrate the muscle to the exterior (D). Mucous glands also develop external ducts that penetrate the hypobranchial muscle in a segmental pattern that does not correlate with that of myotomes (D).

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