976 THE VASCULAK SYSTEM. 



pterygoid plexus in the infratemporal fossa. If the foramen Vesalii is present, the plexus of the 

 foramen ovale is replaced or supplemented by an emissary vein which passes through that foramen. 



(6) Internal Carotid Plexus. The internal carotid plexus accompanies the internal carotid 

 artery through the carotid canal of the temporal bone, and connects the cavernous sinus either 

 with the pharyngeal plexus or with the upper part of the internal jugular vein. 



(7) Plexus of the Hypoglossal Canal. As the hypoglossal nerve passes through the hypo- 

 glossal canal (O.T. anterior condyloid foramen) it is accompanied either by a venous plexus or by 

 a large vein which connects the veins of the medulla oblongata and the lower part of the occipital 

 sinus with the upper end of the internal jugular vein, or with the extra-cranial part of the inferior 

 petrosal sinus. 



VERTEBRAL VEINS. 



The vertebral veins include 



(1) The basi-vertebral veins. 



(2) The external vertebral plexuses. 



(a) anterior fi 



(b) posterior 



(3) The internal vertebral plexus. 



(4) Vertebral longitudinal sinuses. 

 -(5) Intervertebral veins. 



Vense Basivertebrales. The basi-vertebral veins are venous channels, enclosed 

 by endothelial walls, which lie in the interiors of the bodies of the vertebrae. They 

 communicate anteriorly with the plexuses of veins on the anterior surfaces of the 

 bodies of the vertebrae, and they converge, radially, towards the posterior surfaces 

 of the bodies of the vertebrae where they open into the transverse anastomoses 

 between the longitudinal vertebral sinuses. 



Plexus Venosi Vertebralis Extern! The external vertebral plexuses, (a) 

 anterior and (6) posterior. 



(a) The anterior external vertebral plexuses are formed by anastomosing venous 

 channels which lie on the anterior surfaces of the vertebrae. They communicate 

 with the basi-vertebral veins and with the intervertebral veins. 



(6) The posterior external vertebral plexuses lie around the postero-lateral aspects 

 of the vertebras, in the vertebral grooves, around the spines, the articular and the 

 transverse processes of the vertebrae. They communicate with the internal plexuses 

 and with the intervertebral veins, and they open into the vertebral, intercostal, and 

 lumbar veins. 



Sinus Vertebrales Longitudinales. The Longitudinal Vertebral Sinuses. The 

 veins in the interior of the vertebral canal form a network, the vertebral venous 

 network, which lies external to the dura mater and covers the internal surfaces 

 of the arches and the posterior surfaces of the bodies of the vertebrae. The network 

 communicates laterally with the intervertebral veins, posteriorly with the posterior 

 external venous plexuses, whilst anteriorly it receives the basi-vertebral veins. In 

 the anterior part of the network, on the posterior surfaces of the bodies of the 

 vertebrae, at the sides of the posterior longitudinal ligament, there are two large 

 longitudinal channels, the anterior longitudinal vertebral sinuses. Two less marked 

 longitudinal channels, the posterior longitudinal vertebral sinuses, can sometimes be 

 distinguished on the internal surfaces of the vertebral arches. 



The anterior longitudinal vertebral sinuses communicate above with the basilar 

 plexus, the terminal parts of the transverse sinuses, and with the network of veins 

 which accompanies each hypoglossal nerve through the hypoglossal canal. 



The posterior longitudinal vertebral sinuses, when they are well established, 

 communicate above with the occipital sinuses. 



Vense Intervertebrales. The Intervertebral Veins. The internal vertebral 

 venous network is drained not only above into the cranial venous sinuses by the 

 longitudinal vertebral sinuses, but also by a series of intervertebral veins which pass 

 through the intervertebral foramina. In the cervical region the intervertebral veins 

 open externally into the vertebral veins, in the thoracic region into the intercostal 

 veins, in the lumbar region into the lumbar veins, and in the sacral region into the 

 lateral sacral veins. The intervertebral veins convey blood both from the internal 

 vertebral venous plexus and also from the anterior and the posterior external 

 vertebral r>lexuses. 



