Egg Windowing: A Method of Opening Fertilized Chicken Egg Shell to Expose Chorioallantoic Membrane Vasculature

In a fertilized chicken egg, the chorioallantoic membrane or CAM is a highly vascularized layer located below the inner eggshell membrane. It functions to support embryo development.

To expose a fully developed CAM, begin by placing an egg candler - a bright light source - against the eggshell to visualize the egg's interior. Locate the air cell between the outer and inner eggshell membranes and a prominent branching vasculature within the egg. Mark their positions externally.

At these spots, make small circular holes in the eggshell to expose the underlying white shell membrane. Gently pierce the exposed membrane at both locations without disrupting the CAM or causing albumin or blood leakage.

Keeping the egg longitudinally, apply suction over the natural air cell opening to withdraw air from inside. The resulting negative pressure lowers the CAM below the second aperture, generating an artificial air cell over the vascular network.

Outline the relocated air cell. Cut through the eggshell, a few centimeters internal to the outline, without disrupting the air cell-CAM boundary. Remove the incised shell to create a large window, exposing the underlying CAM and vasculature. Use a transparent film to seal the window on viable eggs.