The outlines of anatomy, physiology, and hygiene Being an edition of The essentials of anatomy, physiology, and hygiene, rev to conform to the legislation making the effects of alcohol and other narcotics upon the human system a mandatory study in public schools . fuse the force of a blow. The protection affordedby the shape and structure of the outside por-tion of the skull is very great, and it is a well-known fact in surgery that a blow upon the topof the head, without breaking the bone on whichit falls, may break the bones at the base of theskull, immediately opposite the spot of the blow,
The outlines of anatomy, physiology, and hygiene Being an edition of The essentials of anatomy, physiology, and hygiene, rev to conform to the legislation making the effects of alcohol and other narcotics upon the human system a mandatory study in public schools . fuse the force of a blow. The protection affordedby the shape and structure of the outside por-tion of the skull is very great, and it is a well-known fact in surgery that a blow upon the topof the head, without breaking the bone on whichit falls, may break the bones at the base of theskull, immediately opposite the spot of the blow,. by the mere force of the shock, although the latterbones are much thicker and more massive than theothers. There is only one movable bone in the skull andthat is the loivcr jaiv. If the upper jaw be made tomove in eating or speaking, it is only by movingthe whole head where it joins the neck. 22. Sutures of the Skull.—The bones of theskull are joined together by what are called sutures—i. e., their edges are jagged and irregular, and fittogether like dovetailed boards (Fig. 11). Thisrenders the arch of the skull more compact, and,as far as resistance to pressure is concerned, theV)ones might be considered as one piece, while the3 22 ORGANS OF Fig. II.—General outlines of the skull, sliowing the sutures. interruptions at the sutures tend to deaden theshock of a blow. 23. The Frontal Sinuses.—In the front of the skull there are twocavities in the sub-stance of the boneitself. These aresituated just abovethe eye-brows, andare called Xh^ fron-tal siniLscs (Fig. 12).The layer of boneAvhich forms theirfront wall causesthe prominencesjust over the eye-brows, and, as the cavities increase in size withage, this portion of the forehead becomes moreprominent. The cavities are lined with mucousmembrane, and areconnected with the in-side of the nose by acanal or small passage,so that, when a personhas a severe cold inthe head, the inflam-mationsometimes runsup this passag
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