The chondrocranial key: Fetal and perinatal morphogenesis of the sphenoid bone in primates

The sphenoid bone articulates with multiple basicranial, facial, and calvarial bones, in humans its synchondroses are known to contribute elongation of the skull base possibly cranial angulation. Its early development (embryological, fetal) has frequently been studied a comparative context. However, perinatal events morphogenesis have explored very few primates. Using cross-sectional age sample non-human primates (n=39; 22 platyrrhines; 17 strepsirrhines), we used microcomputed tomographic (µCT) histological methods track changes bone. In midline, expands dimensions at three growth centers, including sphenooccipital, intrasphenoidal (ISS) presphenoseptal (PSept) synchondroses. Bilaterally, alisphenoid is enlarged via appositional that radiates outward from cartilaginous parts during midfetal stages. remains connected basitrabecular process basisphenoid alibasisphenoidal synchondrosis (ABS). Reactivity proliferating cell-nuclear antigen observed all synchondroses, indicating active perinatally. Between mid-fetal birth ages Saguinus geoffroyi , decrease breadth columns chondrocytes. most primates, ABS greatly diminished by birth, likely earliest fuse, although least some cartilage may remain one-month age. Unlike humans, no primate our exhibits fusion ISS. A dichotomy among orientation ABS, which more rostrally directed platyrrhines. Based on fetal specimens, was initially oriented within horizontal plane, redirects inferiorly late These occur tandem forward orbits platyrrhines, combined downward midface. Thus, postulate centers direct midface orbit before birth.