internal carotid, while the complexion of the cheek, the volume of the face, the evolution of the teeth, the eye-brows, and the still small processes of the outer table of the skull, all sufficiently evince that the energy of the circulation has now found a new direction in the branches of the external carotid. All the parts to which this vessel carries blood, are, from henceforth, developed with nearly as much rapidity as the brain had been in the first septennial period of life. But among the bones hereby so rapidly developed, the nasal bones, the spongy portion of the ethmoidal bone, the external table of the os frontis and the ossa malæ, have their full share. But as the growth of all these bones, except the os frontis, is forwards, and as this bone always maintains an exact harmonic continuity with the other bones of the transverse suture, it is necessarily brought forward along with these bones. It cannot carry the diploië along with it, which substance not being so well nourished, will tend to become absorbed. The same effect will be greatly promoted from another cause. The schneiderian membrane growing at the same time with great rapidity, advances through the infundibular passages of the ethmoid bone, is now in immediate contact with the decaying fibres of the diploië connecting the two tables of the frontal bone, which may not yet be absorbed, and passing through amongst these, whilst the pulsation of its vessels causes them to be removed, it gradually scoops out for itself a wedge-shaped cavity between the two tables, which we denominate the frontal sinus. This sinus is not completed till twenty-one, or about the time when the bones of
