Nasal fossa of mouse and dwarf lemurs (primates, cheirogaleidae)

Dimensions of the external midface in mammals are sometimes related to olfactory abilities (e.g., "olfactory snouts" of strepsirrhine primates). This association hinges on the largely unexplored relationship between the protruding midface and internal topography of the nasal fossae. Herein, serially sectioned heads of embryonic to adult cheirogaleid primates (mouse and dwarf lemurs) and a comparative sample were studied. To assess the anteroposterior distribution of olfactory epithelium (OE) within the nasal fossa, the surface area of OE and non-OE was measured in two mouse lemurs (one adult, one infant). Prenatally, ethmoturbinal projections appear in an anteroposterior sequence. Fetal mouse lemurs, tenrecs, voles, and flying lemurs have four ethmoturbinals that project toward the nasal septum. Major distinctions among these mammals include the number of turbinals in recesses and the extent of the olfactory recess. Surface area measurements in the adult mouse lemur reveal that 31% of the entire nasal fossa is lined with OE. The majority is sequestered in a posterior recess (70% OE). Anterior to this space, only 28% of the nasal fossa is lined with OE. Ethmoturbinal I is lined with relatively less OE (35%) compared with more posterior ethmoturbinals (46-57%). Age comparisons support the idea that OE increases less than non-OE between ages. Regionally, results suggest that most growth in surface area occurs in turbinals. But in all ethmoturbinals, surface area of non-OE differs between ages more than that of OE. This study shows that the anterior part of the nasal fossa is mostly nonolfactory in Microcebus murinus.