THE SUPERIOR CAVAL SYSTEM. 



875 



1. The anterior diploic vein (v. diploica frontalis) descends in the diploe of the frontal bone 

 and at the level of the supra-orbital notch opens either into the supra-orbital or ophthalmic vein. 

 It communicates with the anterior temporal diploic vein and also with the frontal veins and the 

 superior longitudinal sinus. 



2. The anterior temporal diploic vein (v. diploica temporalis anterior) passes downward and 

 forward in the diploe of tne anterior portion of the parietal bone and opens either into a deep 

 temporal vein or into the spheno-parietal sinus. 



3. The posterior temporal diploic vein (v. diploica temporalis posterior) passes downward in 

 the diploe of the posterior part of the parietal bone and usually opens into the mastoid emissary 

 vein, thus communicating with the lateral sinus. It also communicates with the posterior auric- 

 ular vein and may open into it. 



4. The occipital diploic vein ( v. diploica occipitalis) passes downward in the squamous portion 

 of the occipital bone, not far from the median line, and opens either into the occipital vein or into the 

 occipital emissary vein, by which it communicates with the torcular Herophili or the lateral sinus. 



Fig. 758. 



Occipital diploic vein 



Posterior 



temporal diploic vein 



•Anterior or frontai 

 diploic vein 



T^rontal \ein 

 Supra-orbital vein 

 Frontal diploic vein 

 Angular vein 



Anterior temporal 



diploic vein 

 Deep temporal vein 



Outer table of skull has been removed to expose venous spaces of diploe. 



Practical Considerations. — The diploic veins being incapable of effective 

 contraction, bleed very freely and persistently, and are sometimes a source of 

 embarrassment during operations on the skull. Through their communications 

 with the veins of the scalp on the one hand, and with the endo-cranial sinuses 

 and meningeal veins on the other, they may, as in some cases of compound fracture, 

 convey infection from the surface to the diploe, causing osteomyelitis and necrosis, 

 or within the cranium, causing septic meningitis or sinus thrombosis. Pyaemia 

 has followed an infective phlebitis of the diploic veins themselves. Diploic infection 

 introduced from without — pyogenic — or through the blood — tuberculous — is apt 

 to spread rapidly within the diploic tissue itself, as well as to the underlying 

 structures. 



The Emissary Veins. 



The term emissary vein is applied to those branches which place the sinuses of 

 the dura mater in communication with veins external to the cranial cavity. Using 

 the term in its broadest sense, the emissary veins are very numerous, since both the 

 diploic and the meningeal veins might be regarded as such, as well as the carotid 



