Veins of the Trunk. 



455 



Processus spinosus 



, Plexus venosus vertebralis 

 / posterior 



Rete venosum vertebrae 



I 



Processus 

 articularis superior 



V. intervertebralis -S-i 



Processus 

 transversus 



Plexus venosi vertebrales 

 interni 



V. basivertebralis 



Corpus 

 vertebrae 



Plexus venosus 

 vertebralis anterior 



494. Spinal veins in a inorizontal section, 



viewed from above. 

 (Only the body of the vertebra has been cut through.) 



Plexus A'enosi xertebrales externi (see also Fig. 493) lie on the external surface 

 of the spinal column and are divisible into anterior, smaller plexuses and posterior, larger 

 plexuses. The plexns reiiosi vertebrales anterior es are best developed in the cervical spine and 

 there lie upon the bodies of the vertebrae and upon the mm. longi capitis et colli; they receive 

 tributaries from the muscles and fi"om the bodies of the vertebrae and are connected lateralward 

 -n-ith the vv. intervertebrales and with the following plexuses. The plexus venosi vertebrales 

 posteriores lie in part directly upon the posterior surface of the vertebral arches, processes and 

 ligaments, in part between the short muscles of the back. They are best developed in the 

 cenical portion (see also Figs. 486 and 4S8) and are connected there especially with the v. 

 occipitalis , v. vertebralis and v. cervicalis profunda ; besides, they anastomose through spaces 

 in the ligamenta flava with the plexus interni and unite in front with the plexus anteriores 

 and with the vv. inteiwertebrales. 



Yv. intervertebrales accompany the nn. spinales in the foramina intervertebralia and 

 lie chiefly in plexuses on their anterior surfaces. They receive the vv. spinales (from the spinal 

 cord), which bear valves at their openings and are connected with the plexus vertebrales interni 

 and exteiTii representing their channels of outflow ; they have valves where they terminate in the 

 neck in the v. vertebralis, or in the trunk in the vv. intercostales, lumbales or sacrales laterales. 



The TV. intercostales (see lig. 495), situated usually singly at the lower margin of 

 a rib in the sulcus costae, close to and above the artery, increase evenly in diameter from 

 above downward. The upper 9 ( 10) form venous circles which empty their contents partly 

 sternalward into the w. mammaria interna and musculuphrenicae (see p. 445), partly vertebral- 

 ward into the system of the v. azygos; at their mouths they carry valves coiTespondingly 

 dii-ected ; from their middle portiuns they send off branches in the 1 st 6th (or 7*^) intercostal 

 spaces to tlie axilla (vv. costouxillaresj (see p. 453). The lower 23 vv. intercostales have 

 no outflow forward and receive tributaries, supplied with valves, from the diaphragm and ft'om 

 the abdominal muscles. Veins of smaller diameter and inconstant in length are to be found 

 also at the upper margin of each rib; they are manifoldly connected with the others. Each 

 V. intercostahs receives a ramus posterior near the bodies of the vertebrae, which is larger 

 than it is itself and which runs near the ramus posterior of the a. intercostalis ; into this 

 flow tributary vessels from the skin and from the muscles of the back, as well as the ramus 

 spinalis, which , as a continuation of the vv. intervertebrales (vide supra), collects the blood 

 from the spinal colimm and its contents. 



