Meeting Abstract
The sphenoethmoidal synchondrosis, or prespheno-septal synchondrosis (PSept), is reported to remain unfused until six to seven years in humans. In non-human primates, it is reported to be fused perinatally. However, only macaques have been studied to date using histology. Here, we examined the hypothesis that humans are unique in prolonged PSept patency using ontogenetic samples of monkeys, strepsirrhine primates (lemurs and lorises), and a comparative sample of other mammals. Specimens ranging from late fetal to one month postnatal age were studied using histology, immunohistochemistry, and micro-computed tomography methods. We found that none of these nonhuman primates lack a PSept at birth, although monkeys have a distinct joint shape. Unlike strepsirrhines and other mammals, monkeys have a convex anterior end of the presphenoid with a radial boundary of endochondral growth. These results show that extended growth at PSept does not distinguish humans from other primates. If synchondroses are significant to the uniquely flexed cranial base angle of humans, other joints would be more relevant (e.g., intrasphenoidal synchondrosis). In a broad sense, the synchondroseal growth patterns reveal a basic dichotomy between strepsirrhines (resembling other mammals) and anthropoids that is more directly applicable to facial form. Our findings imply that the septal cartilage may set the pace of forward midfacial growth at critical time periods, but can also accommodate variations in face shape from the typical mammalian pattern that directs growth of relatively longer snouts.
