THE SKULL. 15 



while playing, was struck by a baseball on the left frontal eminence. A distinct 

 circular depression or cup was produced exactly corresponding to the shape of the 

 ball. There were no symptoms of cerebral concussion, because the force of the 

 blow was expended on the bone and not transmitted to the brain within. As 

 pointed out by Mr. Rickman Godlee, the sutures in very young children being soft, 

 the transmission of the force from one bone to another is prevented. 



The diploic structure of the skull is not well developed until adult age, therefore 

 the bone is homogeneous. It is also elastic, and, particularly in infants, it may be 

 dented without being seriously fractured; these dents are apt to disappear and 

 become level with the surrounding bone as the child grows older. The dura mater is 

 more adherent in children and fractures are, on that account, more liable to tear it 

 and even lacerate the brain beneath. 



Fractures of the Skull in Adults. As adult life is reached the inner and 

 outer tables of the bones become separated, leaving the space between to be filled 

 by the diploic tissue. The diploe consists of cancellous bone in the meshes of which 

 run the diploic veins and capillaries. Both the inner and 

 outer tables are brittle, but the inner especially so. It is 

 also harder and more compact than the outer table. On 

 account of this difference we find in cases of fracture that 

 the inner table is more comminuted than the outer, so that, 

 while the outer may show a single line of fracture, the inner 

 table immediately beneath may be broken into several frag- 

 ments. This is one reason why trephining is so frequently 

 resorted to. 



In rare cases there may be depression of the inner , FIG. 2i.-smaii piece of the 



, , . , J . r i i i skull showing hairs imprisoned 



table With none Of the OUter. A Case Of this kind Occurred in a linear fracture actual size. 



during our Civil War. A soldier, while looking over a ram- 

 part, was struck a glancing blow by a bullet, on the upper anterior portion of the 

 skull. The outer table at the site of injury was not at all depressed, but the inner 

 table had a large piece broken off, which injured the membranes. 



The elasticity of the skull is shown in cases of fracture in which hairs are found 

 imbedded in the line of fracture. Figure 21 is from such a case. A negro was 

 struck on the head by a falling rock and an extensive longitudinal fracture was pro- 

 duced in which many hairs were fastened. About a centimetre from the main frac- 

 ture was a small fissure, not over a centimetre long, and sprouting up out of it, like 

 bushes from the bare ground, were a number of hairs. In such cases the hairs are 

 carried into the line of fracture by the force of the blow; the elastic bone then springs 

 back into place and pinches the hairs, thus holding them in place. 



The bones of the adult skull are very strong and firmly fixed. The sutures 

 begin to unite at the age of forty years and are likely to have disappeared at the age 

 of seventy. Even in young adults the fibrous tissue between the bones has so nearly 

 disappeared that they practically act in transmitting force as one continuous bone. 

 For these reasons slight blows do not cause fractures. It takes a very heavy blow 

 usually to cause a fracture and the force is so great that shock or concussion of the 

 brain with disturbance of its functions is a common symptom. 



The force of the blow is expended first at the point of impact, and if a fracture 

 occurs it usually starts there. From that point it radiates to other portions of the 

 skull, so that fractures of the vault frequently extend to the base. The course 

 pursued by the fracture has been formulated into a law by Aran ; that they take a 

 straight line from the point of impact on the vault to the base of the skull, and are 

 not deflected by the sutures. 



Charles Phelps ("Traumatic Injuries of the Brain") found that in 127 cases of 

 fracture of the base of the skull, 12 implicated the base only. So that, if we are able 

 to say that there is a fracture of the base of the skull, there are over 10 chances to 

 one of its extending up into the vault. In only two were the fractures more than a 

 slight fissure ; so that in a marked fracture of the base there would be 63 chances to 

 one of its extending into the vault. Also, from Aran's law, we see that, if we diag- 

 nose a fracture through the middle ear, we may be pretty sure that the force was 

 applied directly above, and be led to trephine accordingly. 



