DEVELOPMENT OF THE SENSE ORGANS 



375 



(Fig. 369 C, E). The groove deepens and closes caudally to form a tubular struc- 

 ture in the cranial portion of the nasal septum (Fig. 371). During the sixth month 

 it attains a length of 4 mm. Nerve fibers, arising from cells in its epithelium, join 





nifiihiy e 



rihmo-turbinal I 

 A a sal septum 



— Naso-lacrimal dud 

 ' Maxillo-turbinal 



Bun ll ( 1 ily 





'/^. 



Fig. 372. — Transverse section through the nasal passages of a 65 mm. human fetus. X 14. 



the olfactory nerve, and it also receives fibers from the n. terminalis. In late 

 fetal stages it often degenerates, but may persist in the adult (Merkel, Mangakis). 



Hard palal' 



Upper 



^^^A uditory tube 



Fig. 373. — Right nasal passage of a fetus at term (after Killian). /, Maxillo-turbinal; II-VI, ethmo- 

 turbinals. The slight elevation at the left of I and // is the naso-turbinal. 



Special cartilages are developed for its support (Fig. 371). The organ of Jacob- 

 son is not functional in man, but in many animals evidently constitutes a special 

 olfactory organ. 



