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the permanent rudiment,—being, by means of the cord connected with the gum,—gradually assumes the same relation to

Fig. 164. the gum, as was originally sustained by the temporary rudiment.

The ossification of the permanent teeth

commences from the third to the sixth month after birth, for the incisors and first molaris; about the ninth month for the canine teeth; about three years for the second molaris ; at three years and a half for the fourth ; and at ten years for the fifth; but all this is liable to much variation.

The permanent teeth, during their formation, are crowded to gether in the jaw; but as soon as they have advanced to a certain point, and can no longer be contained within their own alveoli, absorption of the anterior parietes of those cavities takes place, and the teeth are allowed to come in some measure forwards. In consequence of such absorption it frequently happens, that not only the socket of the corresponding temporary tooth, but that of the tooth on each side is opened to the permanent one. tion now occurs in the root of the temporary tooth,—generally at the part nearest its successor, and this gradually proceeds as the latter advances, until the root is completely removed, when the crown falls off, leaving room for the permanent tooth to supply its place. It does not seem that this absorption of the root is produced by pressure on the part of the permanent tooth, as it often happens, according to Mr. Bell, that the root of the temporary tooth is wholly absorbed, and the crown falls out spontaneously, long before the succeeding tooth has approached the vacant space. As a general rule, however, the actions must be regarded consentaneous; and Mr. Bell thinks, that this absorption resembles that, already referred to, for the formation of a new cell to receive the permanent pulp, and that it may be termed, like it, a "process of anticipation." In both instances, the existence, though not the pressure, or even the contact, of the new body is necessary to excite the action of the absorbent vessels; and we accordingly find, that in those cases, by no means unfrequent, in which the temporary teeth retain their situation in the mouth, with considerable firmness, until adult age, the corresponding permanent ones have not been formed."

The following are the periods at which the permanent teeth generally make their appearance. They are extremely irregular, however, in this respect, and the estimate must consequently be regarded as a general approximation only.

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Anterior or first great molares,

64 years. Middle incisors,

7
Lateral incisors,

8
Anterior bicuspids, or first lesser molares, 9
Posterior bicuspids, or second lesser molares, 10
Canine teeth,

11 or 12 Second great molares,

12 or 13 Third great molares or dentes sapientiæ, 17 to 20 When these have all appeared, the set is complete, consisting of thirty-two teeth, sixteen in each jaw,—the number of temporary teeth having been only twenty. The accompanying figure represents the upper and lower permanent teeth in their alveoli or sockets, the external alveolar plate having been removed to show the mode in which they are articulated. Fig. 166 represents the same teeth when removed from the socket.

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Whilst the jaws are becoming furnished with teeth and increasing in size, they undergo a change of form, and the branches become more vertical, so as to favour the exertion of force during mastication. When the teeth issue from the gums they are most favourably situated for the act of mastication; the incisors are sharp, the canine pointed, and the molares studded with conical asperities; but, in the progress of age, they become worn on the surfaces that come in constant contact.

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f Q, a. Central incisors.-6,6. Lateral incisors.-C, c. Canine teeth.-d, d. First bicuspidati.-e, e, Second bicuspidati.-f,f. First molares.-8,8. Second molares.-h, h. Third molares or dentes sapientiæ.

During the occurrence of these changes, which embrace the whole of the period we are considering, and extend, at times, into the two next, the animal functions, especially that of sensibility, become surprisingly developed, and the intellectual and moral results of a well adapted system of education are strikingly apparent. The nutritive functions are likewise performed with energy, the body not yet having attained its full growth; and, towards the end of the period, the organs of reproduction commence that development, which we have to describe under the next period.

Sect. III. Adolescence. The commencement of this age is marked by one of the most extraordinary developments that the frame experiences, and its termination by the attainment of full growth in the longitudinal direction. The period of the former of these changes is termed puberty; that of the latter the adult age.

The age of adolescence has been considered to extend from fifteen years to twenty-five in men; and from fifteen to twenty-one in women; but this is only an approximation like the other divisions of the ages, all of which are subject to great fluctuations in individual cases.

During the periods we have considered, no striking difference exists between the appearance of the male and female, except as regards the generative organs; but about the age of puberty essential changes occur that modify the characteristics of the two sexes in a manner which they maintain through the remainder of existence; and these changes affect the whole of the economy to a greater or less degree.

In the male, the skin loses more or less of its delicacy and whiteness; the hair becomes darker, the cellular tissue condensed, and

the muscles more bulky, so that they are strongly marked beneath the surface; the beard appears, as well as hair upon the pubes, chest, and in the axillæ. The different parts of the body become developed in such manner that the centre of the frame now falls about the pubes. The encephalon has increased in size, especially at the posterior and inferior part,—the cerebellum, and has become firmer. The ossification of the bones, in the direction of their length, terminates towards the end of the period. The muscles become more red and fibrinous, losing the gelatinous character they previously possessed, and, in the animal, exhibiting those striking changes which we see from veal to beef, from lamb to mutton, &c.

The larynx undergoes great augmentation, and the glottis particularly is elongated and widened. The jaws complete their growth, and the dentes sapientiæ appear, so as to make up the full complement of sixteen in each jaw. The changes in the nutritive organs are not great, consisting chiefly in their development to correspond with the increased size of the frame. The greatest modification is produced in the organs of reproduction, which are now in a state to exercise their important functions. The testicles, at the period of puberty, suddenly enlarge so as to attain twice the diameter they previously possessed ; and the secretion of sperm is accomplished. The penis is also greatly increased in size; and, according to Adelon, "becomes susceptible of erection." This susceptibility, however, exists long before this age. It may be noticed even in the first period of infancy. The scrotum assumes a deeper colour. Such are the chief changes that supervene in the male.

In the female, they are not quite so striking;—the general habit remaining much the same as during childhood. The skin preserves its primitive whiteness; and instead of the cellular tissue becoming more condensed, and the muscles more marked, as in the male, fat is deposited in greater quantity between the muscles, so that the form becomes more rotund. New hair appears only on the organs of reproduction and in the axillæ, whilst that of the head begins to grow more rapidly. The development of the genital organs is as signal as in the male. The ovaries attain double their previous dimensions; the uterus enlarges; and a secretion takes place from it which has been elsewhere described the menstrual flux; the mons veneris and labia pudendi are covered with hair, the labia enlarge, and the pelvis has its dimensions so modified as to render labour practicable. At an early age, the long diameter of the brim is from before to behind; but it now assumes the opposite direction, or from side to side; and the bosom, which, prior to this age, could scarcely be distinguished from that of the male, becomes greatly augmented; fat is deposited so as to give the mammæ their rotundity; the mammary gland is enlarged; and the nipple of greater size;—changes fitting the female for the new duties which she may be called on to exercise.

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The functions undergo equally remarkable modifications, under the new and instinctive impulse which animates every part of animal life. The external senses attain fresh and peculiar activity; the intellectual faculties become greatly developed, and this is the period, during which the mental character is more modified and improved by education than any other. It embraces the whole time of scholastic application to the higher studies; and prior to the end of the period, the male youth enters upon the avocation which is to be his future support, and both sexes may become established in life in the new relations of husband and wife, and of parent and child. It is during this age, that the indescribable feeling of interest and affection is experienced between individuals of the two sexes; and that the boldness of the male contrasts so strikingly with the captivating modesty of the tender female:

“ That chastity of look, which seems to hang,

A veil of purest light o'er all her beauties.”

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The muscles having acquired their strength and spring, the severer exercises are now indulged, and mechanical pursuits of all kinds, military or civil,—are undertaken with full effect. The expressions participate in the altered condition of the mental and moral manifestations, and indicate vivacity, energy, and enthusiasm. The voice of the male acquires a new character, and becomes graver, for reasons assigned elsewhere; whilst that of the female experiences but slight modification.

The nutritive functions of digestion, absorption and respiration experience but little change; but nutrition, strictly so called, is evidently modified, from the difference which we notice in the development and structure of the various organs. The muscles contain more fibrine; the blood is thicker and richer in globules; and the excretions manifest a higher degree of animalization. Urea has usurped the place of benzoic acid in the urine; and the cutaneous transpiration has lost its acidulous smell, and become rank and peculiar.

Lastly, the sexual functions are now capable of full and active exercise, and appear to be intimately connected with the spirits, energy, and development of many parts of the economy. genital organs do not undergo the due change at puberty, or if the testes of the male or the ovaries of the female be removed prior to this age, considerable modification occurs. This is more manifest in the male, inasmuch as the ordinary changes, that supervene at puberty, are in him more marked than in the female.

The removal of the testicles, prior to puberty, arrests those changes. The beard does not appear, nor the hair in the axillæ or on the pubes, as in the entire male; and if those animals, in which the males are distinguished by deciduous horns, as the stag,—or by crests and spurs, as the cock, be castrated before their appearance, they never present themselves. If, however, they be castrated

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