Morphology and Morphometry of the Deformed Cervical Vertebrae in a Mutant Knotty‐Tail (knt/knt) Mouse

Mice with short and knotty tails arose as a spontaneous mutant in an ICR strain, and they have been named knotty‐tail mouse (gene symbol; knt ). They also have a minor anomaly of the cervical vertebrae, especially in the axis. In this study, the cervical vertebrae of knotty‐tail (knt/knt ) mice were investigated by morphological and morphometric examinations during the prenatal and postnatal period. From the observation of double‐stained preparations of knt/knt mice, morphological changes of cervical vertebrae were confined to the vertebral arch of the axis, which was asymmetrical and hypoplastic. From the morphometric analyses, outside of the axis, minor anomalies (i. e., broadened cervical vertebrae in the transverse direction, shortened and broadened ventral tuberculum of the atlas, thickened ventral lamina of 6th cervical vertebra) were maintained in the cervical vertebrae of knt/knt mice. Morphological deformity, reflecting an adult osseous anomaly, had been already formed in the cartilaginous axis prenatally. In the papain‐digested preparations of knt/knt mice, a bony invagination into the canal was detected in the axis, and the morphometric analyses on axis revealed that the growth of spinous process was apparently disturbed in comparison with that of ICR mice.