SPINAL MARROW. 113 



Mr. Bell the respiratory tract, which, with the anterior, 

 forms what is termed antero-lateral. 



These different columns give origin to different nerves 

 having different endowments. 



FIG. 15. 



The anterior give off 

 the nerves of motion, 

 and the posterior those 

 of sensation, the latter 

 distinguished by hav- 

 ing a ganglion on their 

 root. And the middle 

 portion supplies the respiratory nerves. There is still 

 another set of nerves described by Mr. M. Hall, as having 

 their centre in, and belonging most especially to the spinal 

 marrow, called the excito-motory, or reflex nerves, having 

 an action entirely independent of volition, and conse- 

 quently having the power, as proved by experiment, of 

 producing muscular movement when the brain is absent. 

 The fibres, over which the brain exerts its influence in 

 producing voluntary motion, do not stop in the spinal mar- 

 row, but, according to Mr. Solly, curve upwards and extend 

 to the brain, thus explaining most satisfactorily why it is 

 that apoplexy, by compressing these cerebral fibres, should 

 produce a loss of voluntary motion and sensation, while 

 those that are free and uncompressed in the spinal cord 



FIG. 15. Section of the spinal marrow, with its membranes. 



a Dura mater. 6 6 Dura mater forming a sheath for each of the roots of a 

 spinal nerve, and afterwards a sheath for the nerve itself, c c Sheath around 

 each of the roots of the spinal nerve, by the arachnoid, during its passage 

 through that membrane. The dotted line represents the arachnoid, d Space 

 between two layers of arachnoid, e Space between arachnoid and pia mater. 

 /One of the dentations of the ligamentum-denticulatum. g g Pia mater, h An- 

 terior median fissure, i White commissure connecting the lateral halves of the 

 cord, j Grey commissure connecting the two semilunar processes of gray sub- 

 stance, k Posterior median fissure. 1 1 Antero-lateral columns of spinal cord. 

 m m Two lateral columns, n Posterior columns, o o Posterior median columns. 

 p Origin of anterior or motor root of spinal nerve, q Origin of posterior or 

 sensitive root, r Ganglion on posterior root, s Spinal nerve separating into 

 its two primary divisions, anterior and posterior. 



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