Comparison of spinal sections from wild-type (A) versus ank/ank mice across the intervertebral disc (IVD). (B) A spinal section from an 18-week-old ank/ank mouse. Large fusion masses of fibrocartilaginous tissues extend from one vertebra to the next, at the edges of the annulus fibrosus of the IVD. (C) A larger view of the marked rectangular area from (B). Within the fusion masses, "bone islands" are complete with bone marrow (BM). These regions demonstrate the classic appearance of the growth plate, such as tidemark areas (dotted black arrow) and organized subchondral layers (black arrow). The connective tissue/fibrous tissue masses seen in the ank/ank spine are largely ill defined (yellow arrow).