42 THE NERVOUS SYSTEM 



the dura mater must be traversed before any fluid can be 

 obtained. Whether the fluid obtained is derived from the 

 subdural or from the subarachnoid space seems to be im- 

 material. 



Intracranial Tension. Although it is impossible to deter- 

 mine the condition of the intracranial tension in the adult 

 unless lumbar puncture is performed, it is quite easy to do 

 so in the infant, owing to the presence of the anterior font anelle. 



Post 

 'onfonel/e 



FIG. 24. Foetal Skull, seen from above. QOHNSTONE'S Midwifery.} 



This area is situated at the meeting-place of the two parietal 

 bones with the two halves of the frontal bone, and it forms a 

 diamond-shaped gap in the skull (Fig. 24). When the intra- 

 cranial tension is normal, the bony edges of the fontanelle can 

 readily be palpated and a normal slight pulsation, which is 

 transmitted from the base of the brain, can be felt. This 

 pulsation becomes more noticeable when the intracranial 

 tension is slightly increased, but it disappears entirely when 

 the tension is greatly increased and also when it is lowered. 

 Increased intracranial tension occurs in the acute fevers 



