Chap, viiij THE PALATE. 129 



coalesce with each other and with the septum descend- 

 ing from above in the middle line. . . . When the 

 union of the opposite parts takes place, the naso- 

 palatine canal is left as the vestige of the previous 

 fissures. The median union of the palate begins in 

 front about the eighth week in the human embryo, 

 and reaches the back part, when completed, in the 

 ninth and tenth weeks " (Allen Thomson, in Quain's 

 " Anatomy "). 



In this way the hard and soft palates are formed, 

 and the upper lip completed ; and it will be under- 

 stood that hare-lip and cleft palate depend simply 

 upon imperfect closure of the foetal gap between the 

 nasal and buccal cavities. 



The mucous membrane covering the hard 

 palate is peculiar in that it is practically one with 

 the periosteum covering the bones ; and, therefore, in 

 dissecting up this membrane the bone is bared, as the 

 mucous membrane and the periosteum cannot be 

 separated. The membrane is thin in the middle line, 

 but is much thicker at the sides near the alveoli, the 

 increased thickness depending mainly upon the in- 

 troduction of a number of mucous glands beneath the 

 surface layers, such glands being absent in the middle 

 line. The density and toughness of the soft covering 

 of the hard palate render it very easy to manipulate 

 when dissected up in the form of flaps in the opera- 

 tion for the cleft palate. 



The main blood supply of both the bones of the 

 hard palate and its mucous covering is derived from 

 the descending palatine branch of the internal maxil- 

 lary artery. This vessel, which is practically the only 

 vessel of the hard palate, emerges from the posterior 

 palatine canal near the junction of the hard palate 

 with the soft, and close to the inner side of the last 

 molar tooth. The vessel runs forwards and inwards, 

 to end at the anterior palatine canal. Its pulsations ou 

 J 4 



