Fig. 6. Skeletal phenotype of Hoxa2^-/-, Ptx1^-/- single and Hoxa2^-/-;Ptx1^-/- double mutants. The base of the cranium (A-D), mandible (E-H), squamous bone (IL) and otic vesicle (M-P) of wild type (A,E,I,M), Ptx1^-/- (B,F,J,N), Hoxa2^-/- (C,G,K,O) and Hoxa2^-/-;Ptx1^-/- (D,H,L,P) mutants are shown. In the base of the cranium of Hoxa2^-/- and Hoxa2^-/-;Ptx1^-/- embryos, an extra element associated with the basisphenoid was observed (white arrow in C,D). The mandibles of Ptx1^-/- and Hoxa2^-/-;Ptx1^-/- embryos were smaller (F,H). The squamous bone of Hoxa2 and Hoxa2^-/-;Ptx1^-/- embryos showed an extra element (arrows in K,L). The styloid process (St) and the stapes (S) (which sits in the oval window) were not present in the Hoxa2^-/- and Hoxa2^-/-;Ptx1^-/- embryos (white asterisks in O and P). At least four embryos corresponding to each genotype have been analyzed and showed similar phenotypes.