26 HUMAN EMBRYOLOGY AND MORPHOLOGY. 



these are constantly present in the chimpanzee and in animals 

 with a keen sense of smell. In the human foetus of four months 

 six turbinates are usually present, besides secondary processes in 

 the meatuses beneath them. The uppermost of these, the sixth, 

 becomes the sphenoidal turbinate ; the fifth disappears ; the third 

 and fourth may remain separate or become united ; the first and 

 second form the inferior and middle turbinate processes. The agger 

 nasi (naso-turbinal, Fig. 19), in front of the attachment of the 

 middle turbinate process, is a vestige of the naso-turbinal, a 

 process well developed in most carnivora and animals with a 

 strong scent. The uncinate process, which forms the lower 

 border of the hiatus semilunaris, is continuous at its base 

 with the naso-turbinal. Through the hiatus semilunaris acting 

 as a gutter, the antrum may become a cesspool for a suppurating 

 frontal sinus. 



Nasal Duct. — Although in no way connected with the sense 

 of smell, the nasal duct is closely related to the nasal cavities. 



■frontal sinus 

 lachrymal crest 



pars facialis 



uncinate process/- J' 



Fig. 20—Showing on the inner wall of the Orbit (1) the position of the Infundibulum, 

 (2) the pars facialis lachrymalis. 



It is formed between the lateral nasal and maxillary processes 

 (Figs. 1 and 7). Three bones bound it : the superior maxilla on 

 the outer side, formed in the maxillary process; the inferior 

 turbinate, formed in the cartilage of the lateral nasal process, 

 and the lachrymal, formed over the lateral nasal cartilage, bound 

 it on the inner side. The formation of the palate cuts the duct 

 off from the mouth. The hamulus of the lachrymal varies much 



