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Fig. 1. Developmental anatomy of the thymus. A: The thymus primordia are recognizable at around stage 47 (arrows). C: Transverse section of a stage-47 tadpole, at the level of the pharynx (ph); dorsal towards the top. The thymus primordia (arrows) are located lateral and ventral to the hindbrain (hb), between the eye and the developing inner ear (ie), as seen on a longitudinal section (D). F: Higher magnification view of the right thymic primordium shown in E. Longitudinal section of a stage-47 tadpole, anterior towards the top. G: At stage 50, the thymus primordia have increased in size but retained their dorsolateral position (arrows). G, I: Phase contrast. H: Hematoxylin and eosin staining of the same section. K,L: Expression of p63, an epithelial stem cell factor. I,J are a higher magnification view of G,H. L is a higher magnification view of K. Transverse sections, dorsal towards the top. M,N: At stage 55, the thymus has been extensively colonized by the NC-derived pigment cells (arrows). N is a higher magnification view of the thymus shown in M. Dorsal views, anterior toward the top. O: On a transverse section, the cortex (cx) and me- dulla (md) of the thymus are now clearly distinguishable. The dashed circle outlines the medulla in Q. P and Q are higher magnification views of O. Scale bars (A, D) 1⁄4 500 mm; (B, C, E, G, H, N, P) 1⁄4 200 mm; (F, I, J, K, Q) 1⁄4 100 mm; (M) 1⁄4 2 mm; (O) 1⁄4 1 mm. |
