Growth and Development at the Sphenoethmoidal Junction in Perinatal Primates.

Integration of the sphenoid and ethmoid bones during early postnatal development is poorly described in the literature. A uniquely prolonged patency of sphenoethmoidal synchondrosis or prespheno-septal synchondrosis (PSept) has been attributed to humans. However, the sphenoethmoidal junction has not been studied using a comparative primate sample. Here, we examined development of the sphenoethmoidal interface using ontogenetic samples of Old and New World monkeys, strepsirrhine primates (lemurs and lorises), and a comparative sample of other mammals. Specimens ranging from late fetal to 1 month postnatal age were studied using histology, immunohistochemistry, and micro-computed tomography methods. Our results demonstrate that humans are not unique in anterior cranial base growth at PSept, as it is patent in all newborn primates. We found two distinctions within our sample. First, nearly all primates exhibit an earlier breakdown of the nasal capsule cartilage that abuts the orbitosphenoid when compared to nonprimates. This may facilitate earlier postnatal integration of the basicranium and midface and may enhance morphological plasticity in the region. Second, the PSept exhibits a basic dichotomy between strepsirrhines and monkeys. In strepsirrhines, the PSept has proliferating chondrocytes that are primarily oriented in a longitudinal plane, as in other mammals. In contrast, monkeys have a convex anterior end of the presphenoid with a radial boundary of cartilaginous growth at PSept. Our findings suggest that the PSept acts as a "pacemaker" of longitudinal facial growth in mammals with relatively long snouts, but may also contribute to facial height and produce a relatively taller midface in anthropoid primates. Anat Rec, 300:2115-2137, 2017.