Fig. 6. Skeletal alterations of Ring1B^red/red, Mel18^–/– and Ring1B^red/redMel18^–/– mice. (A) The genotypes are indicated at the top. (Parts a-d) Lateral views of the upper part of the vertebral column. Yellow stars in parts c and d indicate a ectopic arch of the occipital bone. Black arrows in parts b-d indicate ectopic ribs associated with the 7th cervical vertebra. Red arrows indicate the prominent spinous process. Blue arrows in parts b and d indicate the additional ossification center of the sternum implying the anterior shift of the sternum. (Parts e-h) Ventral views of the rib cages. Black arrows in parts f and h indicate ectopic ribs associated with 7th cervical vertebra. (B) Various posterior transformations of the axial skeleton and their penetrance (indicated in parenthesis): (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 in 20th vertebra; (8) L5 or 6S1, formation of the sacro-iliac joint in 25th or 26th vertebra; (9) S4Ca1, appearance of the first caudal vertebra in 29th or 30th vertebra; (10) anterior shift of the sternum as revealed by an ectopic ossification.