NASAL FOSSA OF NONHUMAN PRIMATES

Abstract

The nasal fossa was investigated in four different primate genera i.e., Tupaia glis (tree shrew}, Nycticebus coucang (slow loris), Macaca fascicularis (monkey) and Hylobates agilis (gibbon}, comprising over 100 animals. Methods of study included gross anatomy, light and electron microscopy, histochemistry as well as resection of nerves which were presumed to supply the snout region. Gross morphological studies of the nasal fossa reveal that both tree shrew and slow loris manifest a mammalian-type of nasal fossa with ? lamina transversa and a complicated turbinate system. The tree shrew has, in addition, a frontal recess which is characteristic of the nasal fossa of nonprimate mammals, while the monkey and gibbon have the true primate type of nasal fossa, with the gibbon still retaining some of the primitive characteristics. The two prosimian primates have a naked rhinarium lined by moist glabrous skin as found in ordinary mammals. Moreover, these prosimians possess only serous glands in the respiratory mucosa whereas both serous and mucous glands are present in the monkey and gibbon. An extensive distribution of olfactory mucosa and the presence of vomeronasal organs in tree shrew and slow loris further serve to emphasize the differences between the prosimian and simian primates. Histochemistry of mucins in the nasal mucosa shows that the mucins are chiefly located in the goblet cells of the respiratory epithelium, the serous and mucous glands as well as in the Bowman's glands. Moreever, the primate phylogenetic trend is to produce acid mucins in the goblet cells of the lining epithelium with the underlying sercus glands still producing neutral mucins as in tree shrew and slow loris, followed by serous glands secreting both neutral and acid mucins as observed in the monkey. The final evolutionary trend is to form either serous glands secreting acid mucins or to evolve mucous glands producing similar mucins. Fine structure of the olfactory mucosa reveals an increase in length and numbers of microvilli in supporting cells of the olfactory receptors, whereas in the respiratory epithelium, the tendency is towards a stratification of the epithelium in the higher primates. Fine structure of the vomeronasal receptors shows that there is an increase in their complexity from non-primate mammals to prosimian primates. In the supporting cells and in the non-sensory portions of the vomeronasal organs, the evolutionary trend is towards a regression of cilia and secretary granules. However the structural differences are not of such magnitude as to distinguish taxonomically the tree shrew from the slow loris. Innervation of the snout in the four primates shows a decrease in importance of this region as a tactile organ from tree shrew to gibbon. The naked rhinarium of tree shrew is the most richly innervated, with slow loris having a slightly reduced innervation pattern. The monkey and gibbon exhibit hair end-organs as seen in man. Experimental studies shew that the naked rhinarium, though said to be developed from the fronto-nasal process is supplied by the infra-orbital nerves and not by the ophthalmic nerves which are thought to be the nerves supplying the fronto-nasal process. Finally, this comparative study shows that if only nasal fossa anatomy is taken into account, the tree shrew is more like an ordinary mammal than a primate. Similarly, slow loris nasal fossa also shows these features but to a lesser extent. Thus if slow loris is included in the order primates, it would be difficult to exclude the tree shrew from the primate order on nasal fossa anatomy alone. The two simian primates, however, slow the typical type of primate nasal fossa as seen in man.