In its characteristic infantile form, the face is quite round (short and broad), and, when the child is plump, it often happens that at birth the face is broader than it is long. Seen in profile it is orthognathous, and this orthognathism endures throughout early infancy, because the profile still remains in retreat behind the plane of the protruding forehead; i.e., the facial angle exceeds a right angle, and the mandibular region is further back than the nasal (compare profile of infant).
In the course of growth it may be said in a general way that the facial index diminishes; that is, the numerical proportion between width and height becomes lowered as the face lengthens; while the facial angle changes from somewhat more than a right angle to a right angle, and finally to an acute angle of 75°.
In order to obtain an exact idea of the transformations of the face, children should have their pictures taken, full face and profile, on every birthday, as is already customary in England for the purposes of the carnet maternel, the "mother's note-book."
In the illustrations facing this page we have portraits of the same person taken at successive ages (Figs. 113, 114, 115, 116), i.e., at the age of six months, one year and a half, seven, and lastly twelve years; it will be seen that the face has steadily lengthened.
In this case the individual happens to be noticeably leptoprosopic; but observe the rotundity of the infantile face at the age of six months.
An analogous observation may be made in the case of the girl represented in Figs. 118 and 119, at the age of ten months and thirteen years respectively.
Even in the case of abnormal children the same law holds good; an examination of the three pictures of an incurable idiot boy, taken at the ages of six, eleven, and sixteen years (Figs. 121, 122, 123 facing page ([276])), shows that the face, from being originally rotund has become elongated.[42]
We owe to Binet the most exact and complete studies that exist in anthropologic literature on the subject of the growth of the face. He has made a great number of facial measurements, both of children and young persons of the male sex, from four to eighteen years of age, taking the measurements at intervals of two years. The measurements chosen by Binet are all the possible distances that will serve to give the various widths of the face, the distance of the ear from the various points of the profile, and the heights of the various segments; namely (for an exact understanding of these measurements, see section on Technique), auriculo-mental diameter, auriculo-nasal diameter, auriculo-subnasal diameter, auriculo-ophryac diameter, auriculo-metopic diameter, frontal diameter, biauricular diameter, bizygomatic diameter, length of nose, length of chin, subnase-mental distance, height of forehead.[43]
Binet's conclusions are as follows: the growth of the whole head may be divided into three rhythms: that of the cerebral cranium, that of the face apart from the nose, and that of the nose.