404 Anatomy Applied to Medicine and Sutgery. 



the temporal, in the cerebellar fossae, in the orbital plates 

 of the frontal, and at the floor of the lateral sinuses as 

 they approach the base of the skull. The inner table is 

 thinner, whiter and less regular than the outer and is very 

 inelastic and fragile. 



Diploic and Emissary Veins. In the diploe are 

 numerous venous channels which are of large size but 

 have thin walls composed of endothelium overlying 

 a layer of elastic tissue. These venous channels 

 have no valves but communicate freely with one an- 

 other in the adult (in the foetus, however, each system is 

 distinct), and are arranged as follows: (1) The frontal 

 diploic vein, situated in the anterior part of the frontal 

 bone, terminates in the supra-orbital, a tributary of the 

 frontal vein of the scalp, i.e., it empties outwards. (2) 

 The fronto-sphenoidal, in the lateral part of the frontal 

 bone, terminates in the spheno-parietal sinus which 

 empties into the cavernous, i.e., it empties inwards. (3) 

 The anterior temporal, in the anterior part of the parietal 

 bone ends, after piercing the outer table, in the deep tem- 

 poral veins externally, and in the superior petrosal sinus, 

 a tributary of the lateral, internally, i.e., it empties both 

 outwards and inwards. (4) The posterior temporal, in 

 the posterior part of the parietal bone, ends in the lateral 

 sinus, i.e., inwards. (5) The occipital, in the occipital 

 bone, empties into the occipital vein externally, or into the 

 lateral sinus internally, i.e., outwards and inwards. 



Thus there is seen to be a direct communication be- 

 tween the venous systems outside of the cavity of the 

 cranium and the sinuses inside the cranium. In addition 

 to the above, there is another communication established 

 with the interior of the skull, viz., that by means of the 

 emissary veins. 



