NONHUMAN PRIMATE NASOPHARYNX

Abstract

A comparative anatomy of the nasopharynx of Tupaia glis, Nycticebus coucang, Macaca fascicularis, Symphalangus syndactylus and Hylobates agilis available in South East Asia, was undertaken to note the evolutionary trends exhibited by these primates with reference to the nasopharynx. The results obtained reveal that the anterior portion of the `nasopharynx’ up to the level of the tubal orifices is a backward extension of the nasal cavity while that behind these orifices is a true part of the pharynx. It is, therefore, suggested that the various terms including `nasopharynx’ given to this region, are not strictly applicable. The histochemical studies of the epithelial mucins suggest that there is an increase in the sulfomucin secretions of the nonhuman primate nasopharynx in an ascending scale of phylogeny. Moreover, the study also indicates that among the three types of mucins (neutral, nonsulphated and sulphated), the neutral mucins are the most primitive. The cholinesterase studies show that as the phylogenetic scale is ascended, an increase in ChE and a decrease in AChE contents occur in the neural elements of the nasopharynx suggesting that AChE is perhaps more primitive than ChE. The ultrastructural studies of the normal and regenerating columnar ciliated epithelium show that while basal cells are the progenitors of both goblet and ciliated cells, the differentiation mechanism concerned in the formation of the ciliated cells occur in three district phases, viz:- i) an `indifferent’ stage where the cells contain mucous granules; ii) formation of centrioles and concurrent reduction in the amount of `mucus’ droplets; and iii) rearrangement of centrioles towards the luminal surface of the cells along with simultaneous development of cilia. Finally, some of the features exhibited in the tree shrew nasopharynx are similar to those observed in the other primates investigated. Thus, the inclusion of tree shrew within the order Primates may be justified. Moreover, the monkey, a lower member of the Anthropoidea, presents unique specializations such as the presence of a complete nasopharyngeal septum, well formed bilateral pharyngeal bursac and both subepithelial and intracpithelial nerve plexuses. These features are absent in the other primates investigated. Furthermore, the study also reveals that siamang and dark-handed gibbons, though grouped under the same subfamily Hylobatinae, are distinct from each other in many anatomical features of their nasopharynx.