SI'lXAL CORD 



77.-, 



The axones descending from the ccrclicllum and the brain-stem :ire so mixed \vitli 

 other axones that it is dillicult to determine the sequence of their medulla! ion. The 

 fasciculi containing them also contain axones of the variety in the fasciculi proprii 

 and so show medullat ion early. It is probable that the ascending cerehellar fibres 

 acquire their myelin earlier than the descending. 



BLOOD Sri'i'i.v OK TIII: SPINAL CORD. 



The spinal rami of tlic sacral, luniliar, interred :il. or vertebral .'irtcrics. as the case may he, 

 accompany the spinal nerves through the intervertelinil foramina. traverse the dura mater and 

 arachnoid, anil each divides into a dorsal and a \entral ladicular artery. The.-o aecotnpany the 

 nerve-roots to the surface of I lie cord, and there break up into an anaMomosing plexus in the pia 

 mater. From this plexus are derived three tortuously coursing longitudinal arteries and numer- 

 ous independent central branches, which latter penetrate the cord direct. Of the longitudinal 

 arteries, the anterior spinal artery zigzags along the anterior median fissure and givey off the 

 anterior central branches, which pass into the fissure and penetrate the cord. These branches 

 give off a feu twigs to the white substance in passing, hut their most partial distribution is to 

 the ventral portion of the grey substance. The two posterior spinal arteries, one on each side, 

 course along the lines of entrance of the dorsal root-fibres. They each branch and anastomose, 



Fir,. .574. SEMI-DIAGHAMMATIC REPRESENTATION OF THE BLOOD SUPPLY OF THE SPINAL CORD. 



Dortfil external spinal rr 



Posterior ratlicnltir fin 

 I 



Pn.'tfrior central artery and rein 

 / Posterior spinal artery 



/:/,'. i /, 

 r; VOUS\ 



ru: ATX \ 



PKlill'HKRA L ARTERIAL 

 PLEXUS 



- - Posterior radicular artery 



Intercostal artery 



Anterior raiticillar 

 vein 



l t'zternal 



\ Interim! xj*iu<il ivm 

 Anterior central artery 

 Anterior spinal artery 



Anterior radicu- 

 lar artery 



.V/'/.V.IZ, 



Anterior central rein 



so that often two or more posterior arteries may appear in section upon either side of the dorsal 



root. These give off transverse or central twigs to the white substance, but especially to the 

 grey substance of the dorsal horns. Of the remaining central branches many enter the cord 

 along the efferent fibres of the ventral roots, and are distributed chiefly to the grey substance; 

 others from the peripheral plexus throughout penetrate the cord and break up into capillaries 

 within the white substance. Some of the terminal twigs of these :i\- enter the grey substance. 

 The blood supply of the grey substance is so much more abundant than that of the white sub- 

 stance that in injected preparations the outline of the grey figure may be easily distinguished 

 by its abundance of capillaries alone. The central branches are of the terminal variety, that 

 is. their capillaries do not anastomose \\ ith those of other branches. In the white substance 

 the capillaries run for the most part longitudinally, or parallel with the axones. 



The ri-ninix si/xti-m is ipiite similar to the arterial. The blood of the central arteries is col- 

 lected into corresponding central venous branches which converge into a superficial venous 

 plexus in which are six main longitudinal channels, one along the posterior median sulcus. one 

 along the anterior median lis.-ure. and one along each of the four lines of the nerve-i" 

 Thes.. comprise the dorsal and ventral external spinal veins. 



I he internal spinal veins course along the ventral surface of the grey commissure, ami 

 from the convergence of ceitain of the twigs of the unlirinr << ulrnl riiii. I or untral 



iiiir-cs along the posterior median septum in company with the posterior central artery, and 

 empties into the iin-dinii ilurxal riin. The venous system communicates with the coarser 

 extra-dural or internal vertebral plexus chiefly by way of the radicular veins. 



