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. Author manuscript; available in PMC: 2017 Jan 20.
Published in final edited form as: Differentiation. 2016 Jan 20;91(1-3):1–18. doi: 10.1016/j.diff.2016.01.004

Figure 4.

Figure 4

Optical Projection Tomography of male penile urethral development from 6.5 weeks to 16.5 weeks of gestation. Note the progression of the penile urethral meatus (green arrows) from the scrotal folds at 6.5 weeks to a terminal position on the glans at 16.5 weeks. The open urethral groove (red arrows) is best seen from 9.5 to 13 weeks with clear progression of a proximal to distal fusion of the edges of urethral groove to form the tubular urethra (yellow arrows). At 13 weeks the urethra groove is within the glans penis with the tubular urethral completely formed within the shaft of the penis consistent with the endodermal theory of urethral development. Adapted from Li et al. 2014 with permission.