As a general observation, it may be af firmed, that the growth of the embryo, as well as of the child, both before and at= ter birth, is more rapid in proportion as it is younger.
About the middle of pregnancy, the operation of some vital functions is dis cerned : the secretion of fat and bile com mences. At a more advanced period of utero-geslation, the scalp is covered with a short and delicate hair ; the nails are formed ; the membrana pupillaris de stroyed ; the external car becomes firmer and more elastic ; and the testes de scend.
Besides the important changes in the whole economy which follow parturition, there are certain alterations in the exter nal habit of the body. The down which covers the face at birth disappears ; the rugte of the skin are obliterated ; the anus becomes hidden between the but tocks, which are now gradually formed.
The infant gradually brings into action the faculties of the mind. It perceives and attends to external objects, remem bers, desires, &c. It smiles in the second month, and seems to dream at no great length of time after birth. The organs of sense become more complete in their formation. The bones of the skull be come stronger, and the tontanells are di minished. Dentition commences about the eighth month. The inflint may then be weaned, as his teeth enable him to commence the use of more solid food. About the end of the first year he learns to stand on his feet, and to assume the erect posture, that most distinguishing attribute oldie human body.
When it has now been removed from the breast, and learned the use of the lower limbs, its powers and independ ence increase daily, and receive a vast accession from the developement of ano ther peculiar privilege of the human sub ject, the enjoyment of speech ; by which the tongue, under the direction of the mind, pronounces those ideas which are now become familiar.
At the seventh year the twenty milk teeth begin to fall out, and are succeeded in a gradual progress during the follow ing years by the thirty-two permanent teeth. At this time the memory excels all the other faculties of the mind ; where as about the fifteenth year the powers of imagination begin to prevail. This is the
time of puberty, in which the human sub ject is gradually prepared, by various important changes, for the exercise of the sexual functions. The breasts enlarge in the female, the chin becomes covered with hair in the male, and other similar signs of puberty are noticed in both sex es. The menstrual discharge commences in the softer sex ; and this important era in the economy of the female is marked by an increased expression in the eyes, and redness of the lips, and more mani fest sensible qualities in the matter of perspiration. The seminal secretion be comes active in the male, attended with an increase of the beard, and a deep ening of the voice consequent on a re markable developement of the larynx. The internal and spontaneous calls of na ture now rouse the sexual instinct, for the exertion of which both sexes are pre pared.
No definite and precise period can be assigned_ for the changes which constitute puberty : it varies according to climate and temperament. It is more early in the female than in the male ; but in this climate girls may be said to attain it at the age of fourteen or fifteen, and men at se venteen or eighteen. Soon after these periods the growth of the body is com pleted ; the stature of which varies much in different races, not to mention its varie ties in individuals and families. The epi physes, which have hitherto been dis tinct from the body of the bone, are now completely consolidated with it.
Virility, Manhood, or Adult age, begins from the twenty-first to the twenty-fifth year. If the increase of the body in height have ceased at this time, it grows in other dimensions. The organs become firm and consistent; their functions are per. formed with vigour ; the intellectual and moral faculties are perfected; and the dominion of the judgment succeeds that of the imagination. This period, which is called that of mature age, extends to the fiftieth or fifty-fifth year in men, but not much beyond the forty-fifth in wo. men, in whom it begins earlier. During this cong interval men enjoy all the pleni tude of their existence.