Figure 1: (a) Longitudinal section of FDL tendon from a 3-month old mouse. Tendon is composed of parallel collagen fibers and cells aligned (dark blue) in the direction of fibers. Gliding space is shown. (b) The normal structure of fibrocartilaginous entheses. The 4 zones of tissue at the insertion of the human supraspinatus tendon: dense fibrous connective tissue (CT), uncalcified fibrocartilage (UF), calcified fibrocartilage (CF), and bone (B). Reprinted from Benjamin and Ralphs (1998) [13], 1998, Anatomical Society of Great Britain and Ireland, with permission from John Wiley and Sons. AC, articular cartilage; TM, tidemark. (c) Annulus fibrosus fibers between tail vertebra C1 (shown) and C2 (not shown) from 3-month old mouse, showing entheses.