HIO 



VENOUS SYSTEM. 



1. The anterior superficial spinal (or rachi- 

 dian) veins, include, according to this au- 

 thority, the vena azygos major, the vena azt/gos 

 minor, the trunk of the right and left superior 

 intercostal veins, the lumbar and ilio-luniuar 

 veins, and the lateral and middle sacral veins. 



2. The posterior superficial spinal veins, 

 " form an exceedingly complicated network, 

 the meshes of which surround the spinous 

 processes and laminae, and the transverse and 

 articular processes of all the vertebra;." 



B. The deep or infra-spinal veins comprise 

 the following : 



1 . The veins of the bodies of the vertebrae ; 



2. The great anterior longitudinal veins or 

 sinuses (Willis) ; 



3. The posterior spinal veins and plexuses; 

 all these are external to the " theca verte- 

 bralis :" and 



4. The veins of the spinal cord itself; in- 

 ternal to the theca vcrtebralis. 



Superficial spinal veins. The anterior super- 

 ficial spinal veins have been already described 

 as constituting a part of the azygos system. 



The posterior superficial spinal veins (the 

 dorsi-spinal veins of Dupuytren and Breschet) 

 are derived from the muscles which fill the 

 vertebral grooves, and thus cover the laminae 

 and the spinous and transverse processes with 

 a series of anastomosing vessels. In the neck 

 they form a complicated plexus, from which 

 proceed two large veins (posterior jugular, 

 Cruveilhier), which communicate freely with 

 the vertebral veins, and join the venae in- 

 nominata?. 



From the numerous venous circles and 

 plexuses formed by the " dorsi-spinal " veins, 

 communicating branches are given off, which 

 perforate the ligamenta subflava, or pass 

 through the intervertebral foramina, and unite 

 freely with the deep spinal veins. 



Deep spinal veins. 1 . Veins of the bodies 

 of the vertebrae: (veines basi-vcrtcbiales, Bres- 

 chet), [vide Fig. 361. Vol. III. p. 630.], fire 

 contained in bony canals in the bodies of all 

 the vertebra;, and are analogous to the diploic 

 veins of the cranium. The basi-vertebral 

 veins originate in the canallated tissue of the 

 bone, and form larger trunks, which converge 

 towards the posterior surfaces of the bodies 

 of the vertebrae, where the orifices of the 

 bony canals in which they are contained are 

 very apparent ; on emerging from the vertebrae 

 these veins form a plexus (transverse plexus) 

 interposed between the bones and the pos- 

 terior common ligament of the spine, and 

 from which veins pass laterally to terminate 

 in the anterior longitudinal sinuses. Some of 

 the smaller venous canals pass forwards to 

 open on the anterior surface of the vertebral 

 column, where they anastomose with the su- 

 perficial veins. 



2. The anterior longitudinal sinuses, Willis : 

 (grandes veines racJiidicnnes loiigiludinales an- 

 tcrtaircs, Breschet), [vide Fig. 360. p. 630.] 

 These extend the entire length of the ver- 

 tebral column, under the form of two longi- 

 tudinal veins situated within the spinal canal, 

 along the external margins of the posterior 



common ligament, and consequently between 

 the bodies of the vertebrae and the dura 

 mater, (hence sometimes termed meningo- 

 rachidian veins). Opposite every vertebra 

 these longitudinal vessels are connected to 

 each other by the transverse plexus of the 

 basi-vertebral veins, whilst externally they 

 communicate, by means of branches which 

 pass through the series of intervertebral fora- 

 mina, with the numerous veins which ramity 

 on the exterior of the spinal column, viz., the 

 vertebral, azygos, intercostal, lumbar, sacral, 

 &c. These longitudinal venous channels are 

 neither parallel to each other, nor are they of 

 uniform dimensions; opposite the bodies of 

 the vertebrae they are most closely approxi- 

 mated, whilst corresponding to the interver- 

 tebral foramina they are widely separated, as 

 if drawn outwards by the branches which are 

 here connected with them. Each longitudinal 

 sinus, or " venus plexus," (for occasionally 

 two or more veins enter into the formation of 

 these channels on each side,) might therefore 

 be described as formed of " a series of plexi- 

 form arches, which embrace the pedicles of 

 each vertebra, have their concavity directed 

 outwards and their convexity inwards, and 

 the extremities of which anastomose together 

 opposite the intervertebral foramina, where 

 they communicate with the branches on the 

 outside of the spine."* According to Bres- 

 chet, interruptions occasionally occur in dif- 

 ferent parts of these longitudinal channels, a 

 circumstance which still further authorises 

 this description, in which each venous arch is 

 regarded as a separate trunk, communicating 

 with its fellows of the opposite side, and also 

 with similar branches above and below. 



3. The posterior deep spinal veins (veines 

 longitudinales rachidiennes posterieurcs, Bres- 

 chet) are likewise situated in the interior of 

 the spinal canal, between the posterior sur- 

 face of the dura mater and the front of the 

 laminae. They there form a close interlace- 

 ment of vessels (posterior infra-spinal plexuses) 

 which is most remarkably developed in the 

 upper part of the canal. These veins and 

 plexuses are joined by the posterior superficial 

 spinal veins (dorsi-spinal veins), and they com- 

 municate with the anterior longitudinal sinuses 

 by numerous small lateral branches. 



4. The proper veins of the spinal cord (me- 

 dulli spinales, Breschet) are small tortuous 

 vessels, which form an irregular plexus upon 

 both surfaces of the medulla spinalis between 

 the pia mater and the arachnoid membrane ; 

 they communicate through the foramen mag- 

 num with the petrosal sinuses or cerebellar 

 veins, and give off small branches which pass 

 through the foramina with the spinal nerves 

 to establish communications with the several 

 extra-spinal veins. The veins of the spinal 

 cord are apparently the " venae comites " of 

 the proper spinal arteries. 



" The veins of the spine may be regarded, in 

 reference to the general circulation, as es- 

 tablishing an unbroken communication be- 



* Cruveilhier's Descriptive Anatomy, vol. ii. 

 p. 808. 



