Morphological characterization of the skeletal malformations caused by the Dh gene was carried out. Skeletal preparations from newborn mice of Dh/Dh, Dh/+ and +/+ genotypes, and adult Dh/+ mice were examined. The Dh gene induced skeletal deformities at the axial regions from the thorax to the tail. Attachment of the ribs to the sternum was sometimes irregular, and normal segmentation of the sternum was also disrupted. Abnormal fusion of the ventral part of the rib was observed in some cases. Lumbar vertebrae were fewer in number and abnormal in shape. Although it was rare, a curled tail was also observed due to distortion of the caudal vertebrae.