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HANDBOOK OF PHYSIOLOGY. 



section of the cord towards its upper end, and the number entering it 

 by the anterior and posterior roots of each pair of nerves, it has been 

 shown that in the human spinal cord not more than half of the total 

 number of nerve-fibres entering the cord through all the spinal nerves 

 are contained in a transverse section near its upper end. It is obvious, 

 therefore, that at least half of the nerve-fibres entering it must terminate 

 in the cord itself. 



Gray matter. The gray matter of the cord consists essentially of 

 an extremely delicate network of the primitive fibrillae of axis-cylinders, 

 and which are derived from the ramification of multipolar ganglion cells 

 of very large size, containing large round nuclei with nucleoli. This 

 fine plexus is called Gerlach's network, and is mingled with the meshes 



Fio. 332. Transverse section of half the spinal cord in the lumbar enlargement (semi-diagram- 

 matic). 1. Anterior median fissure; 2, posterior median fissure; 3, central canal lined with epithe- 

 lium; 4, posterior commissure; 5, anterior commissure; 6, posterior column; 7, lateral column; 8, 

 anterior column. The white substance is traversed by radiating trabeculas of pia mater. 9, Fasci- 

 culus of posterior nerve-root entering in one bundle; 10, fasciculi of anterior roots entering in four 

 spreading bundles of fibres; 6, in the cervix cornu, decussating fibres from the nerve-roots and pos- 

 terior commissure; e, posterior vesicular columns. About half way between the central canal and 

 7 are seen the group of nerve-cells forming the tractus intermedio-lateralis; e, e, fibres of anterior 

 roots; e', fibres of anterior roots which decussate in anterior commissure. (Allen Thomson.) v 6. 



of neuroglia, which in some parts is chiefly fibrillated, in others mainly 

 granular and punctiform. The neuroglia is prolonged from the sur- 

 face into the tip of the posterior cornu of gray mattdr and forms a 

 jelly-like transparent substance, which, when hardened, is found to be 

 reticular, and is called the substantia gelatinosa of Rolando. 



The multipolar cells are either scattered singly or arranged in groups, 

 of which the following are to be distinguished on either side: (a) In the 

 anterior cornu. The groups found in the anterior cornu are generally 

 two one at the lateral part near the lateral column, and the other at 



