Pedagogical Anthropology, Maria Montessori [online e book reader TXT] 📗

Fig. 128.

The vertebral column rests upon the sacrum, which is the retro-cotyloid portion of the pelvis, and its pressure tends mechanically to straighten the pelvis (see diagram, Fig. 128). This process of straightening has certain limits, and is dependent upon the form of curvature of the vertebral column; if this is exaggerated, as in lordosis, the weight is thrown further forward, almost over the cotyles; consequently, the elevation of the pelvis is not properly accomplished (low pelvis found in lordotics). If, on the contrary, the lumbar curvature is wanting or reversed (kyphosis), the pressure of the column is thrown backward and the straightening up of the pelvis is exaggerated (high pelvis found in kyphotics). Independently of pathological deformities, there are various forms of lumbar curvature in the vertebral column that are normal oscillations, or oscillations acquired through adaptation.

An exaggerated lumbar curvature or saddle-back is found in children accustomed to carry heavy loads upon their shoulders; a diminished curvature is found in children constrained to remain in a sitting posture for many hours a day. The sitting posture tends to cancel the lumbar inward curve; consequently, while children are in school they are promoting the elevation of their pelvis.

The elevation of the pelvis proceeds rapidly at the fifteenth year, during puberty, when the muscular masses become more solid.

A woman is not fitted for motherhood, even if physically developed, so long as her pelvis has not rotated normally. But if the rotation is exaggerated (due to prolonged sitting posture during years of growth), this is very unfavourable to normal childbirth. In rickets, associated with kyphosis, there is a form of exaggerated rotated pelvis (pubis high). The laborious "modern" childbirth, and the dangerous childbirth in the case of women who have devoted much time to study, must be considered in connection with these artificial anomalies. Free movement and gymnastics have for this reason, in the case of women, an importance that extends from the individual to the species.

The study of the limbs is of great importance, because, although it is the special province of the bust to contain the organs of vegetative life, it is the limbs which render it useful. In fact, it is the lower limbs which control our locomotion and the upper limbs which execute the labour of mankind.

One characteristic of man, equally with that of standing in an erect position, supported only on the lower limbs, is the independence of the upper limbs, which are raised from the ground and relieved of the function of locomotion—a function that still continues in all other mammals, excepting the anthropoid apes, whose upper limbs are extremely long and barely escape the earth, and serve the animal merely as an aid and a support in walking. The birds, although supported on their hind limbs alone, nevertheless have their fore limbs assigned to the sole office of wings for the transportation of their bodies.

Consequently, the free and disposable upper limb, peculiar to mankind, would seem to mark a new function in the biologic scale—human labour.

Anatomy of the Skeleton of the Limbs.—In contrast to the bust, the limbs have an internal skeleton, adapted solely to the function of support (not of protection). The bones are covered with masses of striped muscles, which have as their special function voluntary movement, that is to say, obedience to the brain.

The upper and lower limbs correspond numerically, and the arrangement of the bones is analogous; and this holds true for all the higher vertebrates. The nearest bones, those that are attached to the trunk, are single in all four limbs. Then, just as though branching out, they next double in number, and then multiply successively as we approach the extremities of the limbs. Thus the forearm and the lower leg have two bones, and the hands and feet have many.

In the upper arm we have the humerus, in the thigh the femur, in the forearm the ulna and radius (the ulna is situated on the same side as the little finger and the radius on that of the thumb), in the lower leg the tibia and fibula. Then come the many short bones (eight in the carpus and seven in the tarsus) which in the hand form the wrist or carpus, and in the foot the ankle or instep, the tarsus. These are followed by other long bones (five in the hand and five in the foot), which constitute the metacarpus and metatarsus, and these in turn by the long bones of the phalanges (fingers and toes), which grow successively smaller toward the extremities and are successively named proximal, middle and distal phalanges (phalangettes). These last are missing in the thumb and the big toe. In conjunction with the last phalanges, the fingers and toes are protected by nails.

The Growth of the Limbs.—Recent studies, conducted principally by Godin in France, author of the classic work upon growth, have demonstrated that the long bones of the limbs obey certain special laws of biologic growth.

While a long bone is growing in length it does not grow in width or thickness, and while it is increasing in thickness it does not gain in length; hence the lengthening of the bones takes place in alternate periods; during the period of repose relative to growth in length, the bone gains in thickness.

I have already explained, in connection with the stature, that we owe the growth of the long bones to a variety of formative elements, the cartilages of the epiphyses, which control the growth in length of the long bones, and the enveloping membrane of the body of the bone, the periosteum, which presides over the growth in thickness.

The above mentioned alternation in the growth of the bones must therefore be attributed to an alternation in the action of these various formative elements of the bones.

In the case of two successive long bones (for example, the humerus and radius, the femur and tibia, the metacarpus and phalanges, etc.), they alternate in their growth; while one of them is lengthening, the other is thickening; consequently the growth of a limb in length is not simultaneous in all the bones, but takes place alternately in the successive bones. During the time when the growth devolves upon the longest bone, the limbs show the greatest rate of increase in length, and when, on the contrary, it devolves upon the shortest bone, the growth is less; but in either case it continues to grow.

The growth of the long bones of the limbs proceeds by alternate periods of activity and repose, which succeed each other regularly.

These periods of activity and repose occur inversely in each two successive bones.

The periods of repose from growth in length are utilised for gain in thickness, and reciprocally. The long bones lengthen and thicken alternately, and not simultaneously.

It is only at the age of puberty (fifteenth year) that a complete simultaneity of growth takes place, after which epoch the growth in stature and length of limb diminishes, yielding precedence to that of the vertebral column.

When the complete development of the bodily proportions is attained (eighteenth year), the length of the lower limbs is equal to one-half the stature.

When the upper limbs are extended vertically along the sides of the body, the tip of the middle finger reaches the middle point of the thigh, while the wrist coincides with the ischium (hip-bone). The total spread of the arms is, on an average, equal in length to the stature.

The proportions between the lower limbs and the bust, resulting from the attainment of complete individual development, determine the types of stature: macroscelia and brachyscelia. Since the order of growth as between the two essential portions of stature is now determined, we are able to interpret macroscelia as a phenomenon of infantilism (arrested development of the bust).

Malformations. Excessive Development of the Nearer and Remoter Segments.—But there are other proportions that are of interest to us, within the limbs themselves. Even between the nearer and remoter portions of the limbs there ought to be certain constant relations (indices) that constitute differential characteristics between the various human races and between man and the ape. If the humerus or upper arm is taken as equal to 100, the radius or forearm is equal to 73 in the European, while in the negro it is equal to about 80. Furthermore, it is a well-known fact that excessive length of the forearm is an ape-like characteristic.

Consequently, the measurement of the segments of the limbs is important, and it is made with a special form of calipers; when the index of the segments deviates from the accepted normal figure, this constitutes a serious anomaly, frequently found in degenerates, and it often happens that an excessive development of the remoter segments, the bones of the extremities, explains the excess of the total spread of the arms over the stature, unassociated with the macroscelous type.

Absence of Calf.—In addition to this fundamental deviation from normality, there are other malformations worthy of note that may occur in the limbs. Such, for example, is a deficiency or absence of the calf of the leg. The well-turned leg, which we admire as an element of beauty is a distinctive human trait most conspicuous among the races that we regard as superior. Among the more debased negro races the leg is spindling and without any calf; furthermore, it is well known that monkeys have no calves, and still less do they exist among the lower orders of mammals.

Flat Feet.—Another important malformation relates to the morphology of the feet. Everyone knows the distinctive curve or arch of the foot, and the characteristic imprint which it consequently leaves on the ground. Sometimes, however, this arch is missing, and the sole of the foot is all on the same plane (flat foot). The dark-skinned natives of Australia have flat feet as one of their racial characteristics; in our own race it constitutes an anomaly that is frequent among degenerates. Flat feet may also be acquired as the result of certain employments (butler, door-keeper, etc.), which compel certain individuals to remain much of the time on foot. But in such cases the deformity is accompanied by a pathological condition (neuralgic symptoms and local myalgia). Like all malformations, this may have special importance in connection with infantile hygiene (the position of the pupil, the work done by the children, etc.).

Opposable Big Toe.—Another malformation combined with a functional anomaly, that is never met with as a deformity resulting from adaptation, is the opposable big toe. Sometimes the big toe is greatly developed and slightly curved toward the other toes, and capable of such movement as to give it a slight degree of opposability; hence the foot is prehensile. This characteristic, regularly present in monkeys, is so far developed in certain degenerates as to make it possible for them to perform work with their feet