no SURGICAL APPLIED ANATOMY. [Chap. vm. 



fronton asal process, at the sides by the superior maxil- 

 lary processes, and below by the first visceral arch, 

 around which the lower jaw is formed. The nasal 

 and buccal cavities are one. " The separation of the 

 cavity of the mouth, strictly so called, from the nasal 

 fossse, is effected by the development of the palatal or 

 pterygo-palatal processes of the maxillary plate, which, 

 advancing inwards from the two sides, meet and 

 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 intro- 

 duction 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 cleft palate. 



The main blood-supply of both the bones of the 



