DEVELOPMENT OF THE NOSE. 



717 



off, on the inner sides of the nasal grooves, projections which form 

 the inner nasal processes; these unite with the superior maxillary 

 processes to close in the nostril and form the lip. 



The outer nasal process is a thickening on the outer side of the 

 nasal depression, which, running down toward the superior max- 

 illary process, forms eventually the lachrymal duct. 



The mandibular arch forms the lower jaw, and between this 

 and the superior maxillary process the buccal cavity is developed 

 chiefly by the outgrowth of the surrounding tissue ; the epiblast 



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. tp.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. t./. Fore gut. ch. Notochord. if. Infundibulum. 



lining this becomes thinned away, and the subjacent mesoblast 

 and hypoblast disappear ; and thus the buccal cavity is made 

 continuous 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, how- 

 ever, processes arise from the superior maxillae which grow in- 

 ward, and finally meet one another in the middle line, forming a 

 broad plate of tissue intervening between the nasal cavity above 



