836 THE VASCULAR SYSTEM. 
and inner layers of the dura mater; they receive the blood from the terminal 
cerebral veins. 
DIPLOIC AND MENINGEAL VEINS. 
The diploic veins (vv. diploice) are anastomosing spaces in the cancellous 
tissue of the flat bones of the skull; they are lined by endothelium. The number of 
efferent vessels which emerge from these spaces 18 not constant, but usually there 
are at least four—viz. a frontal, two temporal, anterior and posterior, and an 
oceipital. 
The frontal diploic vein (v. diploica frontalis) is one of the most constant ; it 
drains the anterior part of the frontal bone, and, passing through a small aperture 
in the upper margin of the supraorbital noteh, terminates in the supraorbital 
vein. 
The anterior temporal diploic vein (vy. diploica temporalis anterior) drains the 
Anterior temporal diploic vein 
Posterior temporal 
diploic vein— 
Frontal diploic vein 
Occipital diploie 
vein 
Fic. 581.—THE VEINS OF THE DIPLOE. 
posterior part of the frontal bone, and the anterior part of the parietal bone ; it 
pierces the great wing of the sphenoid, and terminates either in the spheno-parietal 
sinus or in the anterior deep temporal vein. 
The posterior temporal diploic vein (v. diploica temporalis posterior) drains the 
posterior part of the parietal bone; it runs downwards to the posterior inferior 
angle of the parietal bone and terminates in the lateral sinus, to which it passes 
either through a foramen in the inner table of the parietal bone or through the 
mastoid foramen. 
The occipital diploic vein (v. diploica occipitalis) is usually the largest of the 
series ; 1t drains the occipital bone, and terminates either externally in the occipital 
vein or internally in the lateral sinus. 
The meningeal veins (vv. meninge) commence in two capillary plexuses, 
a deep and a superficial. The deep plexus is a wide-meshed network in the inner 
layer of the dura mater. Its efferent vessels terminate in the superficial plexus. 
The superficial plexus les in the outer layer of the dura mater. It consists of 
numerous vessels of uniform calibre which frequently anastomose together, and 
terminate in two sets of efferents; of these, one set terminates in the cranial blood 
sinuses, and the other accompanies the meningeal arteries. The efferent meningeal 
