456 ELEMENTARY PHYSIOLOGY less. 



In consequence of the presence of these fissures, only a 

 narrow bridge of the substance of the cord connects its 

 two halves, and this bridge is traversed throughout its 

 entire length by a minute canal, the central canal of 

 the cord (Fig. 143, 3). 



The lines of attachment of the roots of the spinal nerves 

 divide the cord longitudinally into three parts, called 

 respectively the anterior, lateral and posterior columns 

 (Fig. 143, 8, 7, 6), those roots which arise along the line 

 which is nearer to the anterior surface of the cord being 

 known as the anterior roots ; those which arise along 

 the other line are the posterior roots (Figs. 143 and 

 144). A certain number of anterior and posterior roots, 

 on the same level on each side of the cord, converge and 

 form anterior and posterior bundles, and then the two 

 bundles, anterior and posterior, coalesce into the trunk 

 of a spinal nerve ; but before doing so, the posterior 

 bundle presents an enlargement — the ganglion of the 

 posterior root (Fig. 144, Gn.). 



A transverse section of the sjjinal cord (Fig. 144, B, 

 and Fig. 143), shows further that each half consists 

 of two substances — a white matter on the outside, 

 and a greyish-red substance in the interior. A.nd 

 this grey matter, as it is called, is so disposed 

 that, in a transverse section, it looks, in each half, 

 something like a crescent, with one end bigger than 

 the other, and with the concave side turned outwards. 

 The two ends of each crescent are called its horns or 



half of the figure. C, 1-8, cervical; D, 1-12, thoracic (dorsal); L, 1-5, 

 lumbar; S, 1-6, sacral; Br, brachial plexus; Sc, great sciatic nerve; 

 X, terminal filament of spinal cord. 



a, superior, 6, middle, c. inferior cervical ganglion of the sympathetic 

 system ; of these c is fused with d the first thoracic (dorsal) ganglion. 

 In some animals (dog and cat) the ganglion corresponding tf> c, the 

 inferior cervical ganglion of man, is fused with the upper three thoracic 

 ganglia into a common ganglion called tlie " stellate" ganglion (see Figs. 

 22, 23, St. 6.) and the ganglion corresponding to h, the middle cervical 

 ganglion of man, is in this case known as the inferior cervical ganglion. 



d', the eleventh thoracic sympathetic ganglion ; I, the first lumbal 

 ganglion. The ganglia below ss are the sacral ganglia. 



