Fig. 4. E18.5 skull bone preparations (A-F) of wild-type (A,C,E,G,I) and Fgf8 mutants (B,D,F,H,J) demonstrate abnormal development of the palate (P), palatine (PL), alisphenoid (A) and zygomatic arch (Za). The mandibles of Fgf8 mutants were extremely hypoplastic, sparing only the most distal structures (compare C with D). Defects in the styloid process (Sp), tympanic rings (Tr), stapes, incus (S+I), and malleus (M) are observed as well in mutants (F) when compared with wild type (E). Fgf8 mutants also had abnormal or absent external ears (compare arrow in G with H). Immunohistochemistry for the 2H3 antibody demonstrated that cranial nerves 5, 7, 9 and 10 were fairly well formed in wild type (I), with reduction in Fgf8 mutants (J) of the distal tips (compare arrowheads in I to J), and narrowing of the facial branch of cranial nerve 5 (arrow, J). In addition, nerve 10 had fewer ramifications proximally (compare black arrowhead in I with that in J).