Pedagogical Anthropology - Maria Montessori (best free novels TXT) 📗

Fig. 125.—A = vertex of triangle; B B' = extremities of base, corresponding to the two nipples.

These characteristics of the descent of the thorax are fully established in the period of puberty and are of great importance, since, if not completed, they indicate cases of arrest of development or infantilism.

Quétélet has made a study of the triangulation of the thorax (Fig. 125).

If the two nipples and the sternal incisura are connected by straight lines inclosing an isosceles triangle ABB´, the length of the base in the new-born child is 70 millimetres, and that of the sides BA, B´A is 54 millimetres, and the height 41 millimetres.

In the adult the dimensions are as follows: BB´ = 197 millimetres; AB, AB´= 184 millimetres; and the height = 155 millimetres. Comparing the measurements of the child at birth with those of the adult, we find that the base in the adult is 2.81 times, and the side 3.41 times that of the child; in other words, the sides of the triangle increase far more than the base, and its height in the adult (representing very nearly the entire height of the sternum), is 3.78 times that in the new-born child. Consequently, in the course of its transformation the thorax not only descends, but it is also lengthened in the adult, as compared with the form that it had at birth.

B. Dimensions of Thorax in Relation to Stature.—Besides its descent, there is a second transformation of the thorax, in regard to its volumetric relations to the rest of the body. The perimeter of the thorax and the circumference of the head are pretty nearly equal in the new-born child; if anything, the circumference of the thorax is a trifle less than that of the head; but when it equals it, this is a sign of robustness. In the majority of cases it is not until the second year or thereabouts that the two circumferences become equal. If, however, such inequality should still persist after the child had entered upon the third year, it would constitute a sign of rickets (head too large, chest too narrow).

As to the relations between the thoracic circumference and the stature, it is found that in the child at birth the thoracic circumference exceeds one-half the stature by about 10 centimetres. If the difference is less than 8 centimetres it is a sign of feeble constitution, if it is greater than 10 (for instance, 11 centimetres) it is a sign of great robustness.

This difference disappears little by little; at the age of five years it is already reduced to between 4 and 5 centimetres; at the age of fifteen, the period of puberty, it has wholly disappeared, and the well-known relation between the stature and the circumference of the thorax has become established; the thoracic circumference is equal to one-half the stature (see chapter on Form), and this constitutes Goldstein's vital index:

Vi = (100×Tc)/(S)

As early as 1895, Pagliani published some studies of children, which reveal the physiological importance of the dimensions of the thorax; watching the lives of infants whose measurements he took at the foundling asylum, he observed that the mortality of infants is quite rare when they exceed the above proportions between circumference of chest, head, and stature.

From a study of 452 infants, Fraebelius has drawn the following conclusions:

I. Mortality 21 per cent.; circumference of thorax greater than half the stature by 9.10 centimetres; circumference of thorax less by 1.5 centimetres than perimeter of cranium.

II. Mortality 42.9 per cent.; circumference of thorax greater by 7 centimetres than one-half the stature; circumference of thorax less by 2.8 centimetres than circumference of cranium.

III. Mortality 67.5 per cent.; circumference of thorax greater by 4.5 centimetres than one-half the stature; circumference of thorax less by 4.7 centimetres than the cranial circumference.

The thorax in children of five years and upward ought to be larger by a few centimetres (not more than from 4 to 5) than one-half the stature.

C. Transformations of the Thorax Considered by Itself: Alterations in Shape.

Thoracic Index.—Lastly, the thorax changes its shape in the course of growth. In the new-born child it is very prominent in front, and narrow laterally; in the adult, on the contrary, it is more flattened in its antero-posterior dimension and wider transversely. Consequently the transformation consists in a notable difference in the proportion between the width and depth of the chest, that is, between the antero-posterior and the transverse diameters (see chapter on Technique). This proportion constitutes the thoracic index, which is expressed by the following formula:

Ti = (100A-PD)/TD

and this formula gives an idea of the shape of the thorax.

In the child at birth the antero-posterior diameter is very nearly equal to the transverse; accordingly, the index, at birth, oscillates between 90 and 100.

In the adult, however, the thoracic index is on an average 75; the transverse diameter therefore increases much more than the antero-posterior diameter. According to Quétélet, while the transverse diameter multiplies threefold in the course of its growth, the antero-posterior merely doubles (2.36); in addition to this the thorax also lengthens, as we have already seen.

Proportion, Shape and Dimensions of the Thorax.—In the adult normal man we find the following proportions: The distance between the mammary papillæ is about equal to the antero-posterior diameter of the thorax (hence the papillæ indicate the depth of chest) and is also perceptibly equal to one-half the breadth of the shoulders (measured between the two acromia), which, by the way, is the maximum transverse dimension of the skeleton.

This maximum dimension (the biacromial distance) may be regarded as an index of the skeletal development; and Godin takes its proportion to the transverse thoracic diameter (the horizontal distance between the two vertical lines drawn from the arm-pits, in the plane of the mammary papillæ, see Chapter VII, Technique) in order to estimate the proportional relation between the skeleton and the organs of respiration. Since in the course of growth the thorax broadens, that is, the transverse diameter increases more than the antero-posterior, we should expect to find that in the course of evolution, the difference between the transverse development of the skeleton and the lateral development of the thorax steadily diminishes.

It happens, on the contrary, that from the age of ten years onward, during the whole puberal development, the transverse diameter of the thorax steadily becomes less, as compared with the breadth of the shoulders, so much so that if the difference was at first 97 millimetres, it becomes finally 116 millimetres. According to Godin, this indicates that the thorax does not obey the harmonic laws of the development of the skeleton as a whole, but that, owing to causes of adaptation (the school!) it remains definitely inferior to the development which it might have attained, and consequently results in throwing the organism out of its physiological equilibrium. In fact, if we make men raise their arms, especially men of the student class, a certain hollowness, which is æsthetically displeasing, is revealed along the sides of the thorax. This deficiency is corroborated, according to Godin's studies, by his observation of another correspondence in the measurements of the thorax. In addition to the customary measurements, Godin introduced, besides the well-known and classic thoracic perimeter—which is the circumference taken in the horizontal plane passing through the nipples—two other circumferences: one of them higher up, the subaxillary circumference, which includes a large proportion of the pectoral and dorsal muscles; and the other lower down, the submammary circumference, which determines solely the measurement of the thoracic skeleton, since the intercostal muscles are practically the only ones which descend to this level. These two circumferences are to be considered together, according to Godin, as expressing the relation between the organs of respiration and the muscular mass. In complete repose, the subaxillary circumference is much greater than the submammary; but at the moment of maximum inspiration the latter should become equal to the former; hence, the difference between the submammary circumference in repose and during inspiration furnishes an indirect index of the respiratory capacity, and the subaxillary circumference is a test of individual capacity. Godin notes that inspiration almost never succeeds in attaining an equality between the two circumferences.

Shape of the Thorax.—In regard to the shape, which stands in relation to the thoracic index, it is found to vary according to individual types; in fact the index itself, although showing a mean average of 75, oscillates between the extremes of 65 and 85. As a general rule, the brachycephalic races have a deeper thorax, i.e., having a cross-section of more rounded form; the dolichocephalics, on the contrary, have a more flattened thorax in the antero-posterior direction (these races, such as the negroes, are more predisposed to