Fig. 6. The D-V restriction boundary runs across the chondrogenic condensations. (A-D) Paraffin sections of dorsal clone-containing E14.5 mouse limbs stained for lacZ expression. (B,C) Transverse sections of the specimen shown in A at the indicated positions. (E-J) Immunohistochemical detection of Lmx1b (brown) and ß-gal (blue) on cross-sections of E13.5 digits containing dorsal clones. Circles (B,F,I) indicate the sites of prechondrogenic condensations. Rectangles in E-G indicate the regions shown at higher magnification in H-J. Arrowheads (F) indicate the ventral boundary of Lmx1b expression, which is fading but still visible within the prechondrogenic condensation and coincides with the ventral-most position of lacZ-positive cells.