Fig. 2. Bone histological details of the femur of the eosauropterygian diapsid Proneusticosaurus silesiacus Volz, 1902 (MGU Wr. 4438s), from the Lower Muschelkalk of Poland. Detail of inner cortex, i.e., the medullary region and juvenile bone tissue in normal (A1) and polarized (A2) light. Note the remains of calcified cartilage and small erosion cavities in the medullary region as well as the well vascularized surrounding periosteal tissue; the white arrow marks the sharp line, which separates the endosteal from the periosteal region. Detail of low organized and well vascularized parallel-fibred tissue, here interpreted as juvenile tissue in normal (A3) and polarized (A4) light. Note the mixture of primary osteons, simple vascular canals and a secondary osteon. Highly organized parallel-fibred tissue in the middle cortex showing local accumulation of primary osteons in normal light (A5). Middle and outer cortex in polarized light (A6). Note the highly organized parallel-fibred tissue, which is stratified by thin bright layers formed by multiple rest lines. Detail of inner and middle →