DEVELOPMENT OF THE TEETH. 187 



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

 upon the anterior parietes of those cavities, and CEuise their absorption; so that each tooth 

 is allowed to come forwards, in some degree, into the lower part of the socket of the cor- 

 responding Temporary tooth. The root of the temporary tooth now begins to be absorbed, 

 generally at the part nearest its successor ; and this absorption proceeds as the new tooth 

 advances, until the root of the Milk-tooth is completely removed: when its crown falls off, 

 leaving room for the permanent tooth to supply its place (Fig. 88, p f). This absorption 

 is usually regarded as due to the pressure of the Permanent tooth, but this does not appear 

 to be the case; for it is mentioned by Mr. Bell, that it is not an uncommon occurrence for 

 the root of the temporary tooth to be wholly absorbed, and for the crown to fall out spon- 

 taneously, long before the succeeding tooth has approached the vacant space. The same 

 has been remarked by Mr. Bell, of the cavity in the jaw which is formed for the reception 

 of the sac of the Permanent tooth, at the time that it buds off from that of the milk-tooth ; 

 the excavation being often seen to commence before the new sac is formed. Hence, although 

 the two processes, growth, and absorption, are usually contemporaneous in each instance, 

 they are by no means dependent on each other. Still it would seem that the existence, if 

 not the pressure of the new Tooth is necessary to determine the absorption of the old ; for 

 cases are' not unfrequent, in which the Temporary teeth retain their situation in the mouth, 

 with considerable firmness, until adult age, the corresponding permanent ones not having 

 been formed. 



k. In the successive replacement of the Milk-teeth by the Permanent set, a very regular 

 order is usually followed. The Middle Incisors are first shed and renewed, and then the 

 Lateral Incisors. The Anterior Milk Molars next follow ; and these are replaced by the An- 

 terior Bicuspid teeth. About a year afterwards, the Posterior Milk Molars are shed, and are 

 replaced in like manner by Bicuspid teeth. The Canines are the last of the Milk-teeth to 

 be exchanged ; the development of the new ones not taking place until the 12th year. In 

 the succeeding year, the Second pair of the True Molars appears ; the third pair, or denies 

 sapienti(Z, are seldom developed until three or four years subsequently, and often much 

 longer. It has been recently proposed* (and, from the evidence adduced in its favour, the 

 proposition would seem entitled to considerable attention) to adopt the successive stages in 

 the Second Dentition, as standards for estimating the physical capabilities of Children, es- 

 pecially in regard to those two periods which the Factory Laws render it of the greatest 

 importance to determine, namely, the ages of nine and thirteen years. Previously to the for- 

 mer, a child is not permitted to work at all ; and up to the latter, it may be only employed 

 during 9 hours a day. The necessities or the cupidity of Parents are continually inducing 

 them to misrepresent the ages of their children; and it has been found desirable, therefore, 

 to seek for some test, by which the capability of the Child may be determined, without a 

 knowledge of its age. A standard of Height has been adopted by the Legislature for this 

 purpose ; but upon grounds which, Physiologically considered, are very erroneous ; since, as is 

 well known, the tallest children are frequently the weakliest. According to Mr. Saunders, 

 the degree of advance of the Second Dentition may be regarded as a much more correct 

 standard of the degree of general development of the organic frame, and of its physical 

 powers ; and it appears from his inquiries, that it may be relied on as a guide to the real 

 age, in a large proportion of cases ; whilst no serious or injurious mistake can ever arise 

 from its use. It may happen that local or constitutional causes may have slightly retarded 

 the development of the Teeth ; in which case the age of the individual would rather be 

 under-estimated, and no harm could ensue : on the other hand, instances of premature de- 

 velopment of the Teeth very rarely, if ever, occur : so that there is no danger of imputing 

 to a Child a capability for exertion which he does not possess, as the test of height is con- 

 tinually doing. Moreover, if such an advance in Dentition should occur, it might probably 

 be regarded as indicative of a corresponding advance in the development of the whole or- 

 ganism ; so that the real capability would be such as the teeth represent it. 



/. The following is Mr. Saunders' statement of the Ages at which the Permanent teeth 

 respectively appear. The first True Molars usually make their appearance towards the end 

 of the 7th year. Occasionally one of them protrudes from the gum at 6, or more frequently 

 at 63 years of age ; but the evolution of the whole of them may be regarded as an almost 

 infallible sign of the Child's being 7 years old. In other instances, however, where the tooth 

 on one side of the mouth is freely developed, it is fair to reckon the two as having emerged 

 from their capsule ; since the development of the other must be considered as retarded. This 

 rule only holds good, however, in regard to teeth in the same row ; for the development of 

 the teeth in either jaw must not be inferred from that of the corresponding teeth in the other. 



" The Teeth a Test of Age, considered with reference to the Factory Children." By 

 Edwin Saunders. 



