ovalis, which indicates the site of the original foramen ovale. The fossa ovalis is surrounded by a slightly raised ring, the annulus ovalis, representing the curvilinear edge of the original auricular septum.

The foramen ovale is sometimes completely obliterated within a few days after birth. It often, however, remains partially pervious for several weeks or months. We have a specimen, taken from a child of one year and nine months, in which the opening is still very distinct; and it is not unfrequent to find a small aperture existing even in adult life. In these instances, however, though the adhesion and solidification of the auricular septum is not complete, no disturbance of the circulation results, and no admixture of blood takes place between the right and left sides of the heart; since the passage through the auricular septum is always very oblique in its direction, and its valvular arrangement prevents any regurgitation from left to right, while the complete filling of the left auricle with pulmonary blood, as above mentioned, equally opposes any passage from right to left.

CHAPTER XVIII.

DEVELOPMENT OF THE BODY AFTER BIRTH.

THE newly born infant is still very far from having arrived at a state of complete development. The changes which it has passed through during intra-uterine life are not more marked than those which are to follow during the periods of infancy, childhood, and adolescence. The anatomy of the organs, both internal and external, their physiological functions, and even the morbid derangements to which they are subject, continue to undergo gradual and progressive alterations, throughout the entire course of subsequent life. The history of development extends, properly speaking, from the earliest organization of the embryonic tissues to the complete formation of the adult body. The period of birth, accordingly, marks only a single epoch in a constant series of changes, some of which have preceded, while many others are to follow.

The weight of the newly-born infant is a little over six pounds. The middle point of the body is nearly at the umbilicus, the head and upper extremities being still very large, in proportion to the lower extremities and pelvis. The abdomen is larger and the chest smaller in proportion than in the adult. The lower extremities are curved inward, as in the foetal condition, so that the soles of the feet look obliquely toward each other, instead of being directed horizontally downward, as at a subsequent period. Both upper and lower extremities are habitually curled upward and forward over the chest and abdomen, and all the joints are constantly in a semi-flexed position.

The process of respiration is very imperfectly performed for some time after birth. The expansion of the pulmonary vesicles, and the changes in the circulatory apparatus described in the preceding chapter, far from being sudden and instantaneous, are always more or less gradual in their character, and require an interval of several days for their completion. Respiration, indeed, seems to be accomplished, during this period, to a considerable

extent through the skin, which is remarkably soft, vascular, and ruddy in color. The animal heat is also less actively generated than in the adult, and requires to be sustained by careful protection, and by contact with the body of the mother. The young infant sleeps during the greater part of the time; and even when awake there are but few manifestations of intelligence or perception. The special senses of sight and hearing are dull and inex. citable, though their organs are perfectly formed; and even consciousness seems present only to a very limited extent. Volun tary motion and sensation are nearly absent; and the almost constant irregular movements of the limbs, observable at this time, are evidently of a reflex or automatic character. Nearly all the nervous phenomena, indeed, presented by the newly-born infant, are of a similar nature. The motions of its hands and feet, the act of suckling, and even its cries and the contortions of its face, are reflex in their origin, and do not indicate the existence of any active volition, or any distinct perception of external objects. There is at first but little nervous connection established with the external world, and the system is as yet almost exclusively occupied with the functions of nutrition and respiration.

This preponderance of the simple reflex actions in the nervous system of the infant, is observable even in the diseases to which it is peculiarly subject for some years after birth. It is at this age that convulsions from indigestion are of most frequent occurrence, and even temporary strabismus and paralysis, resulting from the same cause. It is well known to physicians, moreover, that the effect of various drugs upon the infant is very different from that which they exert upon the adult. Opium, for example, is very much more active, in proportion to the dose, in the infant than in the adult. Mercury, on the other hand, produces salivation with greater difficulty in the former than in the latter. Blisters excite more constitutional irritation in the young than in the old subject; and antimony, when given to children, is proverbially uncertain and dangerous in its operation.

The difference in the anatomy of the newly-born infant, and that of the adult, may be represented, to a certain extent, by the following list, which gives the relative weight of the most important internal organs at the period of birth and that of adult age; the weight of the entire body being reckoned, in each case, as 1000. The relative weight of the adult organs has been calculated from

the estimates of Cruveilhier, Solly, Wilson, &c.; that of the organs in the foetus at term from our own observations.

It will be observed that most of the internal organs diminish in relative size after birth, owing principally to the increased development of the osseous and muscular systems, both of which are in a very imperfect condition throughout intra-uterine life, but which come into activity during childhood and youth.

Within the first day after birth the remains of the umbilical cord begin to wither, and become completely desiccated by about the third day. A superficial ulceration then takes place about the point of its attachment, and it is separated and thrown off within the first week. After the separation of the cord, the umbilicus becomes completely cicatrized by the tenth or twelfth day after birth. (Guy.)

cuticle also take place According to Kölliker,

An exfoliation and renovation of the over the whole body soon after the birth. the eyelashes, and probably all the hairs of the body and head, are thrown off and replaced by new ones, within the first year.

The teeth in the newly-born infant are but partially developed, and are still inclosed in their follicles, and concealed beneath the gums. They are twenty in number; viz., two incisors, one canine, and two molars, on each side of each jaw. At birth there is a thin layer of dentine and enamel covering their upper surfaces, but the body of the tooth and its fangs are formed subsequently by progressive elongation and ossification of the tooth-pulp. The fully-formed teeth emerge from the gums in the following order. The central incisors in the seventh month after birth; the lateral incisors in the eighth month; the anterior molars at the end of the first year; the canines at a year and a half; and the second molars at two years (Kölliker). The eruption of the teeth in the lower jaw generally precedes by a short time that of the corresponding teeth in the upper.

During the seventh year a change begins to take place by which

the first set of teeth are thrown off and replaced by a second or permanent set, differing in number, size, and shape from those which preceded. The anterior permanent molar first shows itself just behind the posterior temporary molar, on each side. This happens at about six and a half years after birth. At the end of the seventh year the middle incisors are thrown off and replaced by corresponding permanent teeth, of larger size. At the eighth year a similar exchange takes place in the lateral incisors. In the ninth and tenth years, the anterior and second molars are replaced by the anterior and second permanent bicuspids. In the twelfth year, the canine teeth are changed. In the thirteenth year, the second permanent molars show themselves; and from the seventeenth to the twenty-first year, the third molars, or "wisdom teeth," emerge from the gums, at the posterior extremities of the dental arch. (Wilson.) The jaw, therefore, in the adult condition, contains three teeth on each side more than in childhood, making in all thirty-two permanent teeth; viz., on each side, above and below, two incisors, one canine, two bicuspids, and three permanent molars.

The entire generative apparatus, which is still altogether inactive at birth, begins to enter upon a condition of functional activity from the fifteenth to the twentieth year. The entire configuration of the body alters in a striking manner at this period, and the distinction between the two sexes becomes more complete and well marked. The beard is developed in the male; and in the female the breasts assume the size and form characteristic of the condition of puberty. The voice, which is shrill and sharp in infancy and childhood, becomes deeper in tone, and the countenance assumes a more sedate and serious expression. After this period, the muscular system increases still further in size and strength, and the consolidation of the skeleton also continues; the bony union of its various parts not being entirely accomplished until the twenty-fifth or thirtieth year. Finally, all the different organs of the body arrive at the adult condition, and the entire process of development is then complete.

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