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. 2024 Apr 3;19(4):e0298242. doi: 10.1371/journal.pone.0298242

Fig 10. Femoral Histology of Proterochampsa barrionuevoi PVSJ 606.

Fig 10

(A) General view of femoral histology in plane polarized light (PPL). Letters indicate positions of higher magnification photomicrographs B–F. Anterior is toward the top. Scale bar = 3 mm. (B) PPL image of a thick, highly vascularized cortex (left) that surrounds an open medullary space (right). Sparse perimedullar erosion rooms indicate that bone remodeling occurred in PVSJ 606. Primary radial vascularity with occasional longitudinal and circular anastomoses in an FLB context characterizes most of the cortex. Scale bar = 500 microns. (C) XPL image highlighting the onset of secondary remodeling in the deeper regions of the cortex. Two forms of secondary remodeling are present: an Internal Fundamental System (IFS), indicated by layers of centripetally deposited, avascular lamellar fibered bone (LFB) lining the open medullary cavity (yellow rectangle); and erosion rooms (white rectangle). Scale bar = 250 microns. (D) XPL image in the deep cortex, where a single generation of sparse secondary osteons is present (yellow rectangles). Even in these zones, primary tissue persists. Scale bar = 250 microns. (E) XPL with lambda compensator image documenting transition from middle (top of image) to external cortex (bottom of image). The densely vascularized FLB mid-cortex exhibits a sharp transition to much more poorly vascularized, cyclical deposits of LFB in the external cortex. In the mid-cortex, WFB is indicated by pinker regions, while more organized, LFB surrounding primary osteons (turquoise and orange). Vasculature in the mid-cortex include abundant longitudinal primary osteons with some circular and radial anastomoses. The external cortex exhibits more slowly deposited, mostly avascular LFB (orange). Scale bar = 500 microns. (F) XPL image provides a closer look at the periosteal surface of Proterochampsa. At the periosteal surface, at least six cycles of mostly avascular LFB punctuated by LAGs form an EFS. The EFS signals the attenuation of appositional growth linked with the attainment of skeletal maturity. Scale bar = 500 microns.