THE FACE. 



1381 



er (Fig. 1082). If the premaxillary projection be removed altogether, there is nothing 

 left to support the upper lirj, and the result is an ugly deformity, due to the comparative 

 protrusion and redundancy' 

 of the lower lip. 



Suture between premaxilla and vomer 



x Left nasal cavity 



Nasal septum 



Palatine process of 

 maxilla 



.Horizontal plate of 

 palate bone 



Teeth. The milk 

 teeth begin to appear from 

 the sixth to the eighth 

 month, the first to emerge 

 being the lower central 

 incisors. The first denti- 

 tion is completed about 

 the thirtieth month. 

 Delayed dentition is gen- 

 erally due to rickets. Of 

 the permanent set the first 

 to erupt are the first 

 molars, which appear at 

 the end of the sixth or 

 seventh year; the third 

 molars, the last to appear, piQ< 1082t _ SHOWS ARRANGEMENT OF BONES IN DOUBLE CLEFT PALATE 

 may erupt any time be- (Handbook of Practical Surgery, Bergmann, Brims, and Mikulicz). 



tween the eighteenth and 



the twenty-fifth year, or even later. As the permanent teeth push their way 

 towards the surface, absorption of the roots of the first set takes place, and the first 

 set either fall out of their own accord or are easily removed. Loss of the permanent 

 teeth is followed by absorption of the alveolar margin of the jaw. The tooth 

 sockets are lined by a thin periosteum, which is anatomically continuous with 

 the pulp tissue of the teeth on the one hand and the dense fibrous tissue of the 

 deep layer of the gum on the other. 



The upper incisors and canines and the lower premolars have cylindrical roots, 

 hence in extracting those teeth they should be first loosened by a slight rotatory 

 movement ; the roots of the lower incisors and canines and of the upper premolars 

 are flattened, so that they must be loosened by a lateral movement. The roots of 

 the third molars are convergent, generally welded together and curved backwards, 

 especially in the mandible. The first and second upper molars have three roots 

 which are often divergent. 



Tongue. For practical purposes, as well as on developmental and structural 

 grounds, it is convenient to divide the tongue into an anterior two-thirds the 

 oral part, and a posterior third the pharyngeal part (Fig. 1085). At the junction 

 of the two portions, immediately behind the median vallate papilla, is the foramen 

 caecum, which represents the remains of the upper or pharyngeal extremity of the 

 thyreo-glossal duct. Congenital cysts and fistulce which develop from persistent 

 remains of this tract are always median ; those arising from the upper or lingual 

 portion of the tract are situated above the hyoid bone, whereas those developed 

 from the lower or thyreoid portion are situated below the hyoid bone. The liability 

 of these cysts and fistulee to recur after operation is due to the fact that part of 

 the epithelial tract lies in the substance of the hyoid bone. 



The mucous membrane covering the pharyngeal part is much more sensitive 

 than that covering the oral, hence in using a tongue depressor the instrument 

 should, except under special circumstances, rest only upon the latter region, 

 otherwise a reflex arching of the tongue will be set up, which prevents the operator 

 from obtaining a satisfactory view of the throat. Scattered over the pharyngeal 

 1 part are clusters of lymph follicles (lingual tonsils), which appear on the 

 surface as a number of nodular umbilicated elevations provided with little crypts 

 into which mucous glands open (Fig. 1085). The lingual tonsils are liable to 

 chronic inflammation and hypertrophy, conditions which are often accompanied by 

 a varicose condition of the veins which lie immediately beneath the mucous 

 membrane containing the palatoglossus muscle. To obtain a satisfactory view 



88 & 



