BONES OF THE HEAD.
The bones of the head are divided into those of the skull, the ear, and the face. The skull has eight bones. They are composed of two plates, one above the other, with a porous partition between. These two plates are capable of giving the brain very powerful protection against injury, the outer one being fibrous and tough,the inner one, hard and glasslike, and hence called vitreous. The middle layer has the name of diploe. Its spongy nature deadens the jar from a blow inflicted upon the outer table. In early life, when the bones are tender and yielding, this porous layer is not needed, and is not found.
That the bones of the skull may not easily slip by each other and get out of place, they are dovetailed together in curious lines called sutures. In advanced years, these generally close up, the bones uniting firmly together. In early life they are quite open, the firm bones not covering the whole brain. The opening of the coronal suture in childhood is called a fontanelle. It presents a soft place upon the top of the head, where the finger could be pressed down into the brain. In Figure 4, 1, 1, show the coronal suture on the front and upper part of tl,a skull; 2, the sagittal suture on the top of the skull; and 3, 3, the lambdoidal suture, running down on each side of the back part of the skull.
Figure 5 shows the skull ' bones separated from each other at the
sutures : 1, the frontal bone ; 2, the parietal ; 2, the occipital : 4,
the temporal; 5, the nasal; 6, the malar; 7, the superior maxillary;
8,The Unguis, 9 inferior maxillary. Arnott has demonstrated that the
form of the skull is the best possible for sustaining weights, and
resisting blows. The summit of the head is a complete arch, like that of
a bridge. The ear has four small bones, which aid the sense of hearing.
The bones of the face are fourteen in number. They hold the soft parts
in place, and aid in grinding the food.
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