Fig. 5

Histological details of Andrias spp. tissue. A, lining of the medullary cavity by a layer of endosteal bone in femur ASAGS-0078 in normal and polarized light. B, lining of the medullary cavity by a layer of endosteal bone and a well visible Kastschenkos’s line in femur ASAGS-0077 in polarized light. C, distinct, but only partially preserved annulus, separating an inner tissue, which started highly organized and grades then into loosely organized and coarse parallel-fibered tissue in femur ASAGS-0078 in polarized light. D, thick layer of endosteal bone (yellowish) around the enlarged medullary cavity as well as some resorption and infilling of an erosion cavity by secondary endosteal bone in humerus ASAGS-0106 in polarized light. E, medullary region showing large resorption (i.e. erosion cavities) as well as resorbed areas already infilled by secondary endosteal bone in humerus ASAGS-0101 in polarized light. F, medullary region showing equal resorption and deposition of secondary endosteal bone in femur ASAGS-0100 in polarized light. G, tiny medullary cavity surrounded by minor resorption in humerus ZFMK 97391 in polarized light. Note the distinct Sharpey’s fibers in the right lower corner (black stripes). H, a tiny medullary cavity surrounded by a layer of calcified cartilage in femur ZFMK 97931 in polarized light. I, medullary region surrounded by a layer of endosteal bone and filled by local accumulations of calcified cartilage and chondrocytes (black dots) in humerus ASAGS-0050 in polarized light. J, coarse parallel-fibred tissue in the femur ASAGS-0077 in normal and K, polarized light. Note also the dense network of canaliculi and large osteocyte lacunae (both black). L, from the inner to the outer cortex: increase in organization in already highly organized parallel-fibred tissue in the cortex of femur ASAGS-0317 in polarized light. M, highly organized tissue (double headed arrow) in the innermost cortex of femur ASAGS-0078 in polarized light. Note also the dense network of canaliculi. N, scares (i.e. having left holes in the tissue) of Sharpey’s fibers in humerus ASAGS-0050 in polarized light. O, coarse (dark areas) and highly organized (bright areas) parallel-fibred tissue intermixed in the femur ASAGS-078 in polarized light. P, “holes” in loosely organized parallel-fibred tissue in humerus ZFMK 8568 either representing vascular canals (what we render unlikely due to the lack of characteristics of periosteal vascular canals, see text) or the marginally cut nutrient canal in polarized light. Q, diffuse annuli (bright thin areas) in femur ASAGS-0317 in polarized light. R, distinct LAGs (lines of arrested growth) in the outer cortex of humerus ASAGS-0101 in polarized light. Abbreviations: an, annulus; cc, calcified cartilage; ch, chondrocytes; leb, layer of endosteal bone; Kl, Kastschenkos’s line; r, resorption; seb, eb, secondary endosteal bone