Long bone histology of Nothosaurus species. A-G, thin sections in diaphysial region; A-E, in polarized light; F, G, in normal light. A, humerus of N. mirabilis (SIPB R 54/2), cortex with radial vascular canals with funnel structures. Radial vascular canals undulate and seem to follow the orientation of the Sharpey’s fibers; B, medullary region of femur of N. mirabilis (SIPB R 54/2), showing secondary cancellous bone in the medullary region, consisting of several generations of endosteal lamellar bone; C, inner cortex and medullary region of femur of N. mirabilis (SIPB R 50/1), showing well vascularized LZB. Thick endosteal trabeculae line the medullary region. Large erosion lacunae are visible in deeper cortex; D, inner cortex and medullary region of humerus of Nothosaurus sp. indet. (MHI 1906). Embryonic bone is preserved up to the hatching or birth line (marked by the arrow). The remainder of the cortex is made up of highly vascularized LZB. Towards the center of the bone, a highly birefringent circumferential layer separates the cortical bone from the medullary region. It has partially been resorbed. In the medullary region, there are trabeculae consisting of endosteal bone and a core of calcified cartilage. E, humerus of Nothosaurus sp. indet. (MHI 633). Deposition of the cortex began with embryonic bone up to hatching or birth line (marked by the arrow). Cortical bone consists otherwise of highly vascularized incipient FLB; F, humerus of an adult individual of Nothosaurus sp. indet. (SMNS 84856). LAGs in the cortex (marked by arrows) become more closely spaced towards the bone surface, but there is no EFS in the outermost cortex; G, Endosteal lamellar bone surrounding cores of calcified cartilage in the medullary region of MfN R 174–2. Abbreviations: cc, calcified cartilage, eb, endosteal bone, emb, embryonic bone, fs, funnel structures, sf, Sharpey’s fibres.