DEVELOPMENT OF THE TEETH. 295 



period of its progress. The development of the superior Incisors, however, is 

 retarded by a peculiar cause; so that the inferior incisors have the priority in 

 the time of their completion and appearance. 6. The germs of the "perma- 

 nent" teeth, with the exception of that of the anterior Molar, appear in a direc- 

 tion from the median line backwards. 7. The "milk" teeth originate, or are 

 developed, from mucous membrane. 8. The "permanent" teeth, also originat- 

 ing from mucous membrane, are of independent origin, and have no connection 

 with the "milk" teeth. 9. A Tooth-pulp and its sac must be referred to the 

 same class of organs, as the combined papilla and follicle from which a Hair or 

 Feather is developed. 



288. The following is the usual order, and period of appearance, of the 

 several pairs of "milk" teeth. The four central Incisors first present them- 

 selves, usually about the 7th month after birth, but frequently much earlier or 

 later; those of the lower jaw appear first. The lateral Incisors next show them- 

 selves, those of the lower jaw coming through before those of the upper; they 

 usually make their appearance between the 7th and 10th months. After a short 

 interval, the anterior Molars present themselves, generally soon after the termi- 

 nation of the 12th month ; and these are followed by the Canines, which usually 

 protrude themselves between the 14th and 20th months. The posterior Molars 

 are the last, and the most uncertain in regard to their time of appearance ; this 

 varying from the 18th to the 36th month. In regard to all except the front 

 teeth, there is no settled rule as to the priority of appearance of those in the 

 upper or under jaw; sometimes one precedes, and sometimes the other; but in 

 general it may be stated, that, whenever one makes its appearance, the other can- 

 not be far off. The same holds good in regard to the two sides, in which develop- 

 ment does not always proceed exactly pari passu. The period of Dentition is 

 sometimes one of considerable risk to the Infant's life; and this especially 

 when an irritable state of the nervous system has been brought about by unsuit- 

 able food, unwholesome air, or some other cause of disordered health. In such 

 cases, the pressure upon the nerves of the gum, which necessarily precedes the 

 opening of the sac and the eruption of the tooth, is a fruitful source of irrita- 

 tion; producing disturbance of the whole system, and not unfrequently giving 

 origin to fatal Convulsive affections. These last have been particularly studied 

 by Dr. M. Hall, who recommends the free use of the gum-lancet, as a most 

 important means of prevention and cure; but the Author has no doubt that 

 too much attention has been given to the immediate source of the irritation, 

 and too little to the general state of the system ; and that constitutional treat- 

 ment, especially change of air and improvement of the diet, is of fundamental 

 importance. In infants whose general health is good, and who are not over-fed, 

 Dentition is a source of but very trifling general disturbance ; a slight febrile 

 action, lasting but for a day or two, being all that marks the passage of the 

 tooth through the capsule ; and its eruption through the gum taking place with- 

 out the least indication of suffering or disorder. Any existing malady or abnor- 

 mal tendency, however, is pretty sure to be aggravated during the " cutting of 

 the teeth;" and it is, therefore, of the greatest consequence that the infant 

 should be withdrawn, during this period, from all injurious influences ; and that 

 no irregularity of diet, or deficiency of fresh air and exercise, should operate 

 to its disadvantage. 



289. After the lapse of a few years, the further elongation of the jaw per- 

 mits the appearance of the first true Molar; which, as already remarked, is 

 really a " milk" tooth, so far as its formation is concerned. This commonly 

 presents itself about the middle or end of the 7th year; sometimes preceding, 

 and sometimes following, the exchange of the central Incisors, which takes 

 place about the same time. When the "permanent" teeth have so much en- 

 larged, that they can no longer be contained within their own alveoli, they press 



