THE DEVELOPMENTAL AND MORPHOLOGICAL-STUDIES ON THE NEURAL AND SKELETAL ABNORMALITIES IN THE T BTM TAILLESS MICE/

The crosses, T/ or T/t(w32)Xbtm/btm, give rise to 50% incidence of the tailless mice, development of which was investigated. No difference w as seen in external appearance of the embryos at 9 days of gestation. However, some embryos showed fusion of the notochord and the neural tu be at the posterior part of the body on the histological examination. The prospective tailless individuals were distinguishable from the nor mal littermates by the constriction of the root of the tail at 10 days of gestation. Thereafter, they showed several abnormalities such as t he poor growth of the posterior part of the body, thinning of the tail and a blood blister at the tail tip or in the lumbosacral region. The abnormal embryos of 11-12 days showed severer abnormalities in the me dio-dorsal area, i.e., the notochord was branched or degenerated at se veral places and the neural tube was distorted, duplicated or fused wi th the mesenchyme. All the tailless newborn young had blood blisters o r red scars on the dorsal skin at the middle of the lumbosacral region . Histologically, the spinal cord posterior to the lumbosacral level w as revealed to be severely distorted or duplicated and completely devo id of the bony vertebrae, and the dorsal blood blister was found to be the meningomyelocele derived from the abnormal development of the spi nal cord. Skeletal abnormalities of the tailless young were as follows . The sacral and caudal vertebrae were absent. The cervical vertebrae were mostly normal, but the thoracic and lumbar vertebrae showed sever al abnormalities such as fusion of the ribs, lack of the vertebral bod y and vertebral arch.