Growing skeleton in a mouse foetus

A 16-day old mouse foetus that has been stained to highlight the skeleton. The blue stain shows cartilage, while the red indicates areas that have started to form bone. The other tissues have been partly dissolved by chemicals to show this more clearly. This image is a photograph taken with a macro lens and lit from behind. The foetus measures about 20 mm in length.

Katherine Robertson, Department of Anatomy and Developmental Biology, University College, London.