192 



THE HEAD AND NECK 



floor of the stomodceum. From the dorsal part of the man- 

 dibular arch the maxillary process grows forwards, but above 

 and behind it is separated from the lateral nasal process by the 

 naso-maxillary fissure,, a part of which subsequently forms the 

 orbit (Fig. 55). 



These processes fuse so that the median nasal process gives 

 rise to the nasal septum, the os incisivum (premaxilla), and the 

 philtrum (middle third) of the upper lip. The lateral nasal pro- 

 cesses form the roof and sides of the nose, while the maxillary 

 processes form the cheeks and the remainder of the upper lip. 

 At a later date the palatal processes grow medially from the 

 maxillary processes, and unite with the remains of the median 



Nasal septum 



Inferior conch; 



Anterior cranial fossa 



Crystalline lem 

 of the eyeball 



alatine process 

 ental lamina 



Man 

 Meckel's cart 



Dental lamina 



FIG. 56. Frontal Section through the Face ol a Human Embryo 

 at the Seventh Week. 



nasal process and with one another. Fusion occurs anteriorly 

 at first and then spreads backwards. 



Prior to their fusion, the lateral nasal and maxillary pro- 

 cesses are separated from one another by a groove which extends 

 from the region of the orbit to the olfactory pit. This groove 

 becomes converted into the naso-lacrimal (nasal) duct, but if 

 the fusion of the lateral nasal and maxillary processes is incom- 

 plete, the duct opens out on the surface of the face, a rare 

 condition, known as colobomafacialis. 



The conditions of Harelip and Cleft Palate are brought 

 about by two or more of the above-mentioned processes failing 



