VEINS OF THE VERTEBRAL COLUMN 



665 



column is drained by the vertebral, intercostal, lumbar and sacral veins either 

 directly or by means of (3) the intervertebral veins. 



1. The external vertebral venous plexuses [plexus venosi vei'tebrales externi] include the 

 following : 



(o) The anterior vertebral venous plexuses [plexus venosi vertebrales anteriores] (fig. 

 524) consist of small veins ramifying in front of the bodies of the vertebrae. These veins com- 

 municate with the basivertebral veins and are larger in the cervical region than elsewhere. 



(b) The posterior vertebral venous plexuses [plexus venosi vertebrales posteriores] (fig. 

 524) are situated around the transverse, articular, spinous processes and laminae of the vertebrae. 

 Communications take place between the plexuses of each segment and with the veins of the 

 neighbouring muscles and integuments. Branches are also sent, through the ligamenta flava, 

 to the internal vertebral venous plexuses, and, between the transverse processes, to the inter- 

 vertebral veins. 



2. The internal vertebral venous plexuses [plexus venosi vertebrales interni] (fig. 524) : — 

 (a) The two longitudinal vertebral sinuses [sinus vertebrales longitudinales] run through- 

 out the entire length of the vertebral canal. They are situated behind the bodies of the vertebrae 

 on either side, between the bone and the posterior longitudinal ligament. The sinuses have 



( 



Fig. 524. — The Veins op the Vertebral Column. 



Mammillary process 

 ftccessory 

 process or tip 

 of the true 

 transverse 

 process 



Costal ele 



Posterior transverse 



branch 



Posterior vertebral 

 plexus 



External spinal veins 

 Intervertebral vei 



Anterior transvers 

 vein 



Lumbar vein 



Longitudinal verte- 

 bral sinus 



Basivertebral veins 



Anterior 



ral plexus 



extremely thin walls, and their interior is made irregular by numerous folds but no true valves 

 are present. The calibre of the longitudinal sinuses is reduced by constrictions opposite the 

 intervertebral discs; the constrictions alternating with dilatations opposite the vertebral bodies. 

 At each dilatation there occurs a cross communication between the longitudinal sinuses of 

 either side, and each receives a basivertebral vein from the corresponding vertebral body. 

 Opposite every intervertebral foramen and anterior sacral foramen each longitudinal sinus 

 is joined by the corresponding intervertebral vein. The longitudinal sinuses communicate 

 very freely with one another, and with the vertebral retia. At the foramen magnum they 

 communicate with the basilar plexus and, by means of the rete canalis hypoglossi, with the 

 internal jugular vein. 



(b) The venous rete of the vertebrae [retia venosa vertebrarum] (fig. 524) extend from the 

 foramen magnum to the coccyx. They consist of two main retia situated posteriorly and 

 laterally to the dura between the latter and the vertebral arch. They communicate very 

 freely with one another across the median line; with the posterior external plexus by means 

 of twigs perforating the ligamenta flava; and with the longitudinal vertebral sinuses by means 

 of lateral branches. At the foramen magnum they communicate with the occipital sinus. _ 



(c) The external spinal veins consist of two sets — anterior and posterior — which are drained 

 by means of veins following the nerve roots, into the internal vertebral venous plexus. 



The anterior external spinal veins [w. spinales externae anteriores] form a tortuous anas- 

 tomosing vessel in the region of the anterior median fissure. 



The posterior external spinal veins [vv. spinales externae posteriores], smaller than the an- 

 terior run longitudinally on the posterior surface of the cord. 



The external spinal veins form a wide-meshed plexus in the pia mater which drains the 

 internal spinal veins [vv. spinales internae] (see Spinal Cord). 



