THE FACE, MOUTH AND PHARYNX 193 



to unite with one another. In the simplest variety, the maxillary 

 process of one side fails to unite with the mesial nasal process 

 on the surface only, giving rise to unilateral harelip. When the 

 failure is more pronounced, a gap exists between the maxilla 

 and the premaxilla in addition to the harelip. In cleft palate 

 the palatal processes have failed to unite with one another or 

 with the nasal septum. As the fusion occurs latest posteriorly, 

 the bifid uvula is the simplest variety of this defect. The less 

 complete the fusion, the further forward does the cleft extend. 

 Thus the palatal processes may unite with the mesial nasal 

 process but not with one another, in which case the cleft is 

 confined to the soft palate. A greater degree of deformity is 

 seen when, in addition to failure of the palatal processes to unite 

 posteriorly, one palatal process has failed to fuse with the nasal 

 septum. In this case the floor of the nasal fossa on one side is 

 wanting, and the fossa communicates with the mouth. Double 

 cleft palate is the highest degree of this deformity. It is found 

 when the palatal processes fail to unite with one another pos- 

 teriorly and both fail to unite with the median nasal process 

 (i.e. nasal septum and premaxilla). The os incisivum (pre- 

 maxilla) separates the two clefts anteriorly and renders the 

 complete cleft Y-shaped. In these cases double harelip is usually 

 present also, and the clefts extend from the surface to the 

 tip of the uvula. In making the relief incision in the operation 

 for cleft palate, care must be taken not to cut too far postero- 

 medially, lest the palatine artery, which enters the posterior 

 part of the muco-periosteal flap, be injured. 



In making a prognosis with regard to the after-results of 

 closure of a cleft palate, the shape of the arch must be taken 

 into consideration, as the flaps are subjected to less tension when 

 the palatal arch is pointed than when the arch is flat. The 

 degree of tension may be diminished by fracturing the pterygoid 

 hamulus (hamular process) (Stiles). By this means the tensor 

 veli palatini (tensor palati), which winds round the bony process, 

 is thrown out of action. 



Development of the Tongue. Soon after the appearance 

 of the branchial arches (p. 148), a small elevation, the tuber culum 

 impar, appears in the floor of the primitive mouth. Two lateral 

 swellings arise in connection with the mandibular arches and 

 surround and fuse with the tuberculum impar. In this way 

 the anterior two thirds (or oral portion) of the tongue are formed. 

 About the same time a transverse ridge appears behind the 



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