64 



GENERAL ANATOMY. 



Fijr. 32. 



the gray substance into both the lateral and anterior columns. "Within the 

 gray substance, they run longitudinally upwards and downwards ; transversely 



through the posterior commissure to the oppo- 

 site side ; and into the anterior cornu of their 

 own side (Figs. 31, 32). 



The anterior roots are attached exclusively to 

 the anterior column, or rather to the anterior 

 part of the antero-lateral columns ; for there is 

 no antero-lateral fissure dividing the anterior 

 from the lateral column. Within the gray 

 substance, the fibrils cross each other, and di- 

 verge in all directions, like the expanded hairs 

 of a brush (Figs. 31, 82), some of them run- 

 ning more or less longitudinally upwards and 

 downwards; and others decussating those of 

 the opposite side through the anterior com- 

 missure in front of the central canal. 



All the fibres of both roots of the nerves 

 proceed through the white columns into the 

 gray substance, with, perhaps, the exception 

 of some which appear to run longitudinally 

 in the posterior columns ; but whether these 

 latter fibres of the posterior roots ultimately 

 enter the gray substance of the cord after a 

 very oblique course, or whether they proceed 

 upwards to the brain, is uncertain. 



The Central Canal of the Spinal Cord. In 

 the foetus, until after the sixth month, a canal, 

 continuous with the general ventricular cavity 

 of the brain, extends throughout the entire 

 length of the spinal cord, formed by the clos- 

 ing-in of a previously open groove. 



In the adult, this canal can only be seen at 

 the upper part of the cord, extending from the point of the calamus scriptorius, 

 in the floor of the fourth ventricle, for about half an inch down the centre of 

 the cord, where it terminates in a cul-de-sac; the remnant of the canal being 

 just visible in a section of the cord, as a small, pale spot, corresponding to the 

 centre of the gray commissure ; its cavity is lined with a layer of cylindrical 

 ciliated epithelium. In some cases, this canal remains pervious throughout 

 the whole length of the cord. 



The Ganglia may be regarded as separate and independent nervous centres, 

 of smaller size and less complex structure than the brain, connected with each 

 other, with the cerebro-spinal axis, and with the nerves in various situations. 

 They are found on the posterior root of each of the spinal nerves ; on the pos- 

 terior or sensory root of the fifth cranial nerve ; on the facial nerve ; on the 

 glosso-pharyngeal and pneumogastric nerves ; in a connected series along each 

 side of the vertebral column, forming the trunk of the sympathetic ; on the 

 branches of that nerve, and at the point of junction of those branches with the 

 cerebro-spinal nerves. On section, they are seen to consist of a reddish-gray 

 substance, traversed by numerous white nerve-fibres : they vary considerably 

 in form and size ; the largest are found in the cavity of the abdomen ; the 

 smallest, not visible with the naked eye, exist in considerable numbers upon 

 the nerves distributed to the different viscera. The ganglia are invested by a 

 smooth and firm closely-adhering membranous envelope, consisting of dense 

 areolar tissue.; this sheath is continuous with the neurilemma of the nerves, 



Longitudinal section of the white and 

 gray substance of the spinal cord, through 

 the middle of the lumbar enlargement. 

 (Magnified 14 diameters.) 



