Fig. 8. Skeletal alterations seen in Ring1B^red/red, Mel18^–/– and Ring1B^red/redMel18^–/– mice on the compound genetic background. (A) Respective genotype of Ring1B and Mel18 loci are indicated at the top. For Ring1B^red/redMel18^–/–, three specimens are shown. (Parts a-f) Lateral views of the upper part of the vertebral column are shown. Stars in parts c and e indicate ectopic floating bone or ectopic arch of the occipital bone, respectively. Arrows in parts b, c, e and f indicate ectopic ribs associated with C7. (Parts g-l) Ventral views of the rib cages are shown. In part k, ectopic ossification center of the sternum as a consequence of complete anterior shift of the sternum and complete ectopic ribs are indicated by a blue arrow and black arrows, respectively. Note 7th ribs are articulated with the sternum in Ring1B^red/redMel18^–/– mice. (Parts m-r) Ventral views of the thoracolumbar region are shown. Prospective T12 and T13 are indicated by respective numbers. Prospective lumbar vertebrae are indicated by red stars individually. (B) The frequency of the posterior transformations of the axial skeleton is schematically represented. The following parameters are scored and frequency of each alteration is indicated in parentheses: (1) supraoccipital boneC1, appearance of the ectopic bones seen in the craniodorsal region of the C1 vertebra or ectopic arch of the occipital bones; (2) C1C2, presence of the odontoid process on the C1 vertebra; (3) C2C3, lack of the odontoid process from the C2 vertebra; (4) C7T1, appearance of cervical ribs on C7; (5) T1T2, prominent spinous process on T1; (6) T7T8, dissociation of 7th rib from the sternum; (7) T13L1, loss of the rib on 20th vertebra; (8) L1T13, appearance of the rib on 21st vertebra; (9) L5 or 6S1, formation of the sacro-iliac joint in 25th or 26th vertebra; and (10) S4Ca1, appearance of the first caudal vertebra in 29th or 30th vertebra.