18 SURGICAL ANATOMY OF THE CRANIUM. 



ble to inflammation ; which circumstance explains the 

 formation of secondary deposits of pus in various parts 

 of the body, most frequently in the lungs and liver. The 

 brittleness of the internal layer is of surgical importance 

 from the fact that, in blows on the head, it is more lia- 

 ble to be fractured than the outer ; and cases have oc- 

 curred where it has been broken without any apparent 

 depression whatever of the external, giving rise to symp- 

 toms of compression which would otherwise have been 

 difficult of explanation. The diploe is not easily dis- 

 tinguished in young persons. In the application of the 

 trephine, the varying densities of the layers of the skull 

 must be borne in mind, as the pressure upon the instru- 

 ment on its first application must be firm and steady, 

 until the external table is perforated, when there is less 

 resistance. When it is quite perforated the blood of the 

 diploe will be seen in its teeth. The pin of the trephine 

 is now to be withdrawn, to avoid its being pushed 

 through the inner table into the dura mater and en- 

 cephalon ; the inner table, though thinner, will be found 

 to offer more resistance to the saw edge. There are cer- 

 tain localities in the skull where the application of the 

 trephine should be avoided. These are over the lon- 

 gitudinal sinus, the anterior inferior angle of the parietal 

 bone, because of the middle meningeal artery, over the 

 occipital tuberosity, and over the sutures. 



The arrangement of the various sutures of the bones 

 forming the vault of the cranium has greater interest 

 for the obstetrician than the surgeon, as any peculiari- 

 ties connected therewith exist normally only in foetal 

 life or early childhood. The bones of the skull in the 

 fetus or newly-born child are flexible, and between their 

 undeveloped sutures are the fontanettes, the position of 



