THE CRANIUM. 



Frontal sinuses 



is not of great importance. In opening the skull with the chisel or in trephining no attempt is 

 made to avoid them. 



At the thin places in the cranium, such as the squamous portion of the temporal bone, the 

 bottom of the posterior cranial fossa, etc., the diploe is 'absent and the two tables are in contact 

 with each other. The diploe may also undergo more or less atrophy in the aged. 



In the frontal bone the two tables become widely separated on either side of the glabella 

 enclosing the frontal sinuses, which, next to the maxillary sinuses, are the largest of the accessory 

 air-cavities in communication with the nose (see Fig. 3). Between the inner table and the an- 

 terior wall of the frontal sinus there is still a thin layer of diploic tissue, while the inner (posterior) 

 wall of the frontal sinus is formed by the 

 inner table. The frontal sinuses are paired 

 cavities and are separated by a bony 

 septum which is not often situated exactly 

 in the median line. Incomplete septa 

 projecting inward very frequently make 

 these sinuses multilocular, in which case 

 they may attain an enormous size. The 

 sinus opens into the middle nasal fossa 

 (see Fig. 19), but the orifice can rarely be 

 sounded from the anterior nares during 

 life. In the dreaded catarrh of the frontal 

 sinuses with subsequent empyema, it con- 

 sequently follows that relief must be given 

 by chiseling through the bone above the 

 supraorbital margin, never forgetting that 

 the anterior wall of the sinus is much 

 thicker than the posterior one (see Fig. 4). 

 After this has been done, an attempt may 

 be made to re-establish the normal com- 

 munication with the nasal cavity from 

 above. The opening of the frontal sinus 

 from without may lead to a subcutaneous 

 emphysema of the frontal region, since the air from the nasal chambers gains access to the 

 subcutaneous tissues of the forehead. Large frontal sinuses frequently extend posteriorly into 

 the roof of the orbit. The severe pain attendant upon catarrhal inflammation of the frontal 

 sinus is explained by the rich supply of the lining mucous membrane from the nasal nerve. 



The fontanelles are membranous portions of the vertex of the fetus and of the newborn at the 

 junction of several bones where ossification takes place at a comparatively late date. We dis- 

 tinguish two single and two paired fontanelles (see Fig. 5). 



The single fontanelles are the most important : 



i. The large or frontal fontanelle.This is diamond-shaped, and in the new-born is situated 

 between the still ununited halves of the frontal bone and the two parietal bones. Like the frontal 



FIG. 3. The skull with the closed frontal sinuses exposed by 

 chiseling away the outer table and the diploe. 



