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 observation of serial sections and macroscopic observation with whole-mount differential staining of bone and cartilage were performed on day-17 to -22 embryos. The following unusual findings were obtained: (1) The sphenoethmoidal commissure formed a part of the posterior edge of the tectum 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 cartilage and also contributed to formation of the carotid foramen. (3) The hypophysial cartilage consisted of one medial and a pair of lateral cartilage nodules. The homology of the pair of cartilages with polar cartilages in lower vertebrates is discussed.