DIGESTIVE SYSTEM. 



141 



relations is readily obtained. It will be seen that 

 the line of contact between each lateral protuberance 

 and maxillary process forms a groove, the naso-optic 

 furrow or lacrimal groove, which later closes to form 

 the lacrimal canal. The line of contact between 

 each globular protuberance and the maxillary pro- 

 cess is less close, and places each nasal pit in wide 

 communication with the mouth. A failure of union 

 in the latter case causes the deformity of harelip, 



Median triangular por- 

 tion of palate. 



Dental ridge. 



Lateral portion of 

 palate. 



Fig. 102. Roof of the oral cavity of a human embryo with the fun- 

 daments of the palatal processes (after His). 



which may be double or single, depending on 

 whether both or only one side is involved. 



About the fortieth day, in the human embryo, the 

 maxillary processes have grown so far toward the 

 median plane that they have met and united with 

 the lateral and also the median protuberances of the 

 nasofrontal process. The nasal pits are thus sepa- 

 rated externally from the oral fossa. With this 

 union the arch of the upper jaw is complete, but the 



