HUMAN EMBRYOLOGY AND 

 MORPHOLOGY. 



CHAPTER I. 



DEVELOPMENT OF THE FACE. 



Processes which form the Face.— About the middle of the 

 first month of foetal life, five processes begin to spring from the 

 base of the primitive cerebral capsule, which, by the end of the 

 second month, have completely united together to form the facial 

 part of the head. In figure 1, a diagrammatic representation is 

 given of the condition of these five processes about the end of 

 the first month. Of the five, one, the nasal or fronto-nasal, 

 composed of symmetrical right and left halves, is median, and pro- 

 jects beneath the fore-brain; the others are lateral, two on each side, 

 the mandibular and maxillary. The cavity which these five 

 processes surround is the stomodaeum (Fig. 1). It ultimately 

 forms the nasal and part of the buccal cavities. The part of 

 the adult face formed by each process is shown in figure 2. 



Malformations of the Face. — These processes may fail to 

 unite in the second month and in this manner malformations of 

 the face are produced. The most common anomaly is a partial 

 failure of the nasal and maxillary processes to fuse, various 

 degrees of hare lip and cleft palate being thus caused. In hare 

 lip, the cleft appears in the upper lip between the middle part 

 formed by the middle nasal processes and the lateral parts formed 

 by the maxillary processes (Fig. 2). In cleft palate, the failure 

 of union occurs between the deep parts of the nasal and maxillary 



