Fig. 5. Middle ear skeletal phenotype of Hoxa2^-/-, Ptx1^-/- and Hoxa2^-/-;Ptx1^-/- mutants. Stained middle ear skeletal elements from wild-type (A), Hoxa2^-/- (B), Ptx^-/- (C,E) and Hoxa2^-/-;Ptx1^-/- (D,F) were dissected out. (B) In Hoxa2^-/- embryos the malleus (M), incus (I) and tympanic ring (TR) were duplicated in mirror image disposition (M*, I* and TR*). The gonial bone was abnormally extended (G*). (C) In Ptx1^-/- embryos, the tympanic ring was slightly deformed and there was an extra ossified mass (asterisk). (D) In Hoxa2^-/-;Ptx1^-/- only the tympanic ring was not duplicated. The arrowhead points to a small chondrogenic mass associated to the duplicated malleus. (E,F) The same structures as in C and D but without the extra ossified mass. At least four embryos corresponding to each genotype have been analyzed and showed similar phenotypes.