Ill 



THE DIGESTIVE SYSTEM 



THE TEETH 



IN man and most mammals the teeth which serve during 

 the early years of life are deciduous and disappear before the 

 onset of puberty. 



The DECIDUOUS TEETH begin to erupt between the sixth and 

 the ninth months, but their appearance may be considerably 

 delayed in constitutional diseases, of which rickets is by far 

 the most common. The teeth of the mandible usually appear 

 slightly earlier than those of the maxilla, but corresponding 

 teeth on the two sides should erupt at practically the same 

 time. The first teeth to appear are the central incisors, and 

 they are soon followed by the lateral incisors. The first 

 molars erupt early in the second year, and the interval between 

 the first molar and the lateral incisor is filled up by the 

 eruption of the canine, about the eighteenth month. The 

 appearance of the second molar at the end of the second or 

 the beginning of the third year completes the deciduous set. 

 As the teeth make their way through the mucous membrane 

 of the gums, they may, by stimulation of the sensory branches 

 of the trigeminal nerve, give rise to reflex disturbances, which 

 vary from slight malaise to severe convulsive fits. 



The PERMANENT TEETH begin to erupt during the sixth 

 year, and the first to appear is the first molar tooth, which 

 comes to the surface of the gum behind the second deciduous 



molar. As a result of this arrangement, the child is able to 



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