The most obvious distinguishing features are the deepening of the lens pit, with a narrowing of it's outer pore-like opening, and the first appearence of the physiological umbilical hernia. The 1st branchial arch is conspicuously divided into it maxillary and mandibular components. There is advanced development of the brain tube and the tail elongates and thins.

Absent: nasal pits.

10.5 dpc (range 10-11.25)
35-39 somite pairs

All scale bars in microns

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