DEVELOPMENT OF THE NOSE. 



721 



lining this becomes thinned away, and the subjacent mesoblast 

 and hypoblast disappear ; and thus the buccal cavity is made con- 

 tinuous with that of the alimentary canal. 



The cavities of the nasal depressions at first open into the buccal 

 cavity by means of the nasal grooves ; after a time, however, pro- 

 cesses arise from the superior maxillae which grow inwards, and 

 finally meet one another in the middle line, forming a broad plate 



FIG. 301. 



Vertical section of the head of an embryo of a rabbit. (Mihalkovics.) 

 In A. there is no connection between the buccal cavity and the fore-gut. In 

 B. the connection is established. m. Epiblast of neural canal, h. Heart. 

 c. Cavity of fore-brain, me. Cavity of mid-brain, mo. Cavity of medulla. 

 sp.o. Spheno-occipital parts of the basis cranii. sp.e. Spheno-ethmoidal part 

 of the basis cranii. be. Part of basis cranii which receives the pituitary body. 

 am. Amnion. py. Part of heart cavity going to form the pituitary body. 

 i.f. Fore-gut, ch. Notochord. if. Infundibulum. 



of tissue intervening between the nasal cavity above and the buc- 

 cal cavity below. The palate when complete in front gradually 

 closes towards the back of the buccal cavity, and here the com- 

 munication between the nose and the pharynx is left. 



Imperfect development of these parts gives rise to the common 

 congenital deformities, cleft-palate and hare-lip. 



The first cleft is the hyo-mandibular ; it forms the tympano- 

 Eustachian cavity, which becomes separated from the surface by 

 the closure of its outer end by the growth of the membrana tym- 



