1048 



HUMAN ANATOMY. 



Fig. 



Posterior sulcal 



Parasulcal 



Postero-lateral 



Penetrating 



artery 



As these stems pass downward, they are joined and reinforced by the segmental 

 spinal branches gi^•en off by the vertebral, intercostal, lumbar and lateral sacral 

 arteries, which enter the spinal canal through the intervertebral foramina and, after 

 piercing the dura and giving off small r-adieular branches to the nerve-roots them- 

 selves, divide into ventral and dorsal branches that follow the respective nerve-roots 

 to the cord, where they join with the longitudinal trunks which they thus assist in 

 maintaining. By the junction of horizontal branches arising from these arteries, a 

 series of complete annular anastomoses is formed around the cord, which is still 

 further enclosed by additional vertical stems resulting from the union of upward and 

 downward coursing twigs. In this manner, in addition to the large single anterior 

 spinal trunk (Jractiis aiicriosus spinalis anterior^ in the mid-line in front and the 

 paired postero-lateral trunk ipractus arteriosus postero-lateralis spinalis) just in 

 advance of the dorsal nerve-roots, smaller longitudinal arteries are formed at the 

 side and in the vicinity of the nerve-roots. 



From the arterial net-work within the pia, the nervous tissue is supplied by pene- 

 trating twigs that enter the surface of the cord at various points. 



The gray matter receives its principal blood-supply from the series of anterior 

 Jissural arteries, over two hundred in number, which pass from the anterior spinal 

 trunk backward within the median fissure to its bottom and there divide into right 



and left branches, which traverse the 

 9'J3- anterior white commissure to gain the 



gray matter on either side of the central 

 canal. These vessels, the snlco-viar- 

 ginal arteries, divide into ascending 

 and descending branches that provide 



V M^ y'^' l^Vi' fT^ ^y' — 'x ^'■'^^'■y for the entire gray matter with the 



«\a I ,\ / 1 \v V -rjft^iw/. > -^ x/ exception of the most peripheral zone. 



The latter, together with the white 

 matter, receives its supply from 

 the penetrating branches that come 

 from the surrounding intrapial trunks 

 and enter the surface of the cord. 

 Unpaired horizontal twigs, the pos- 

 terior  sulcal arieries, follow the 

 posterior median septum at different 

 levels for some distance, but before 

 reaching the posterior commissure 

 usually break up into terminal ramifi- 

 cations, some of which pass to the 

 gray matter of the posterior horns. 

 Communications exist between the 

 penetrating twigs of the radicular 

 arteries and the lateral branches of the 

 anterior fissural. After entering the nervous tissue, however, each artery provides 

 the sole supply for some definite part of the cord ; they are therefore "end-arteries," 

 a fact which explains the extensive and elaborate system of vessels necessary to 

 maintain the nutrition of the cord. 



The plexiform veins within the spinal pia are formed by the union of the small 

 radicles that collect the blood from the intraspinal capillaries and, after an independ- 

 ent course similar to that of the arteries but not accompanying them, emerge at the 

 surface of the cord. From the venous net-work within the pia six main longitudinal 

 trunks are differentiated. These are : — the unpaired anterior median vein, in front of 

 the corresponding fissure ; the paired antero-lateral veins, just behind the ventral 

 nerve-roots — these two sets receiving the tributaries emerging from the median fissure 

 and in the vicinity of the anterior root-fibres ; the unpaired posterior median vein, 

 behind in the mid-line ; and the paired postero-lateral veins, just behind the dorsal 

 roots. The blood is conveyed from these intrapial channels chiefly by the radicular 

 veins, following the nerve-roots, which communicate with or terminate in the anterior 

 and posterior longitudinal spinal veiiis within the vertebral canal, from which the 



Penetrating 



artery 



Anterior 



fissural Anterior Ascending branch 

 spinal artery 



Part of transverse section of injected spinal cord 

 vascular supply of white and gray matter. > 



showing 



10. 



