DEVELOPMENT OF THE CHONDROCRANIAL BASE OF THE MUSK SHREW, SUNCUS-MURINUS (INSECTIVORA)

To reveal the developmental process of the chondrocranial base of the musk shrew, Suncus murinus (Insectivora), light microscopic observatio n of serial sections and macroscopic observation with whole-mount diff erential staining of bone and cartilage were performed on day-17 to -2 2 embryos. The following unusual findings were obtained: (1) The sphen oethmoidal commissure formed a part of the posterior edge of the tectu m nasi, implying that the posterior portion of the paries nasi in the mammalian nasal capsule shares a common origin with the neurocranium. (2) The processus alaris arose independently from the hypophysial cart ilage and also contributed to formation of the carotid foramen. (3) Th e hypophysial cartilage consisted of one medial and a pair of lateral cartilage nodules. The homology of the pair of cartilages in lower ver tebrates is discussed.