Other abnormalities are revealed by the facial profile. They are due either to total or partial prognathism (already analysed), or to orthognathism, where the facial angle equals or exceeds a right angle; such a profile occurs in cases of hydrocephaly or of macrocephaly in general, usually resulting from infantile arrest of development.
The Evolution of the Face.—The human countenance, that is so marvellously beautiful in our superior hybrid races, passes, during its embryonal life, through many forms that are very far removed from such perfection.
Figures 110, 111, and 112 represent the evolution of the face in animals and in man: and the complete evolution of a woman's face from the embryo during the first weeks of its formation to the attainment of old age.
The embryonal face, as may be seen even better in animals than in man, is surmounted by the brain divided and differentiated into its superimposed primitive vesicles; furthermore, it consists of one single, widespread cavity, at the sides of which may be discerned two diminutive vesicles or bulbs, which are offshoots of the brain and constitute the first rudiments of the eyes. In studying a more advanced stage of development, we may note in what constitutes the upper lip of this wide facial cavity, two nasal ducts or furrows, which are the first indications of the nose.
The principal differentiation which takes place in the face consists of the development from its two lateral walls on left and right, of two thin plates or laminæ that advance across the cavity itself, in its anterior portion, and proceed to unite in a median ridge, the raphe palati; this constitutes the formation of the palatine vault, which is destined permanently to divide the single cavity into two cavities—an upper or nasal, and a lower or buccal cavity. If this process of formation is not completed, the result is a grave abnormality, the cleft palate, popularly known in Italy as a "wolf's throat," and consisting in the fact that the nasal and buccal cavities to a greater or less extent open into each other; this abnormality, due to an arrest of embryonic development, is almost always accompanied by a hare-lip.
Simultaneously with the formation of the palatine vault, another and vertical septum is formed, which divides the upper cavity into two halves, right and left. This division, however, is limited to the anterior portion; the three cavities thus formed have no such division in the rear, but all three open into the gullet or œsophagus, which represents the only relic of the single original cavity.
The maxillary bones are formed in a manner analogous to that of the nasal and palatal septa, through extroversions destined to become ossified.
It is not until later that the external nose is formed (middle of the second month of embryonal life).
After this, the evolution of the embryo becomes evidently a perfectionment and a growth, rather than a transformation.
In the new-born child the face is extremely small in comparison with the cerebral cranium.