Affiliation: | (1) Department of Anatomy and Developmental Biology, University College London, Medawar Building, London, WC1E 6BT, UK Tel.: 0171–387–7050 ext. 2124; Fax: 0171–380–8349; e-mail: ucgaker@ucl.ac.uk, GB;(2) Department of Anatomy, University Medical School, Teviot Place, Edinburgh, EH8 9AG, UK, GB |