The CAM of a 12-day-old chick embryo incubated for 4 days with a gelatin sponge loaded with (A), (C) the angiogenic basic fibroblast growth factor (FGF-2) or with (B), (D) FGF-2 plus VBL 0.75 pmol/L. Note sub (A) numerous blood vessels converging like spokes toward the sponge after India ink injection, whereas in sub (B) there are very few vessels around the sponge or converging toward it. (C) Histologic section of the sponge at the boundary with the CAM mesenchyme shows several canalized, dilated vessels (arrowheaded) intermingled in a collagenous matrix among the trabeculae. (D) No vessels are observed in the histologic section of the sponge at the boundary. Bar, (A), (B) = 8 mm; (C), (D) = 90 μm.