NERVOUS SYSTEM AND GENERAL SENSATION. 



where they enter the brain or spinal cord as roots of nerves, 

 they pass immediately into the white medullary fibres, or cen- 

 tral parts, and at the same time become by one-half, or even 

 two-thirds, smaller. The primary fibres of the brain and 

 spinal cord, as well as those of the olfactory and auditory 

 nerves, are in some cases so delicate, that they measure but 

 the 1 - 1 000th of a line in diameter : frequently, however, they 

 are thicker, from the 1 -400th to the 1-5 00th of a line in 

 diameter. These fibrils, of different dimensions, are constantly 

 observed running over, and under, and near to one another. 



(Figs. 9, 10, B, and 

 11, C.) Examined in 

 the most recent state 

 possible, they are, for 

 the major part, cy- 

 lindrical, but in part 

 also knotty or vari- 

 cose, inasmuch as 

 they exhibit little oval 

 or rounded enlarge- 

 ments in their course. 



(Figs. 9, B, H,A,B.) 

 It is doubtful whe- 

 ther or not this vari- 

 cose state is acciden- 

 tal only, or is really 

 peculiar to certain 

 primary fibres in the 

 living state. So much 

 Fig. 11. A, primary fibres of the olfactory is certain, that the 

 nerve of man. B, a primary fibre from the tho- knots are constantly 

 racic portion of the spinal cord of man. C, a seen arisin * under 

 thin slice from the outer aspect of the ophthalmic , f & , j 



ganglion of man. After Valentin. tne e ? e ? " 



server, and that they 



are frequently effects of the methods of investigation pur- 

 sued. There is nevertheless this peculiarity to be noted in re- 

 gard to the primary fibres of the central parts, that they are 

 much more apt to assume the varicose condition than those 

 of the periphery a peculiarity that seems to be connected with 

 their structure. The sheaths, in fact, of the central primary 

 fibres are much more delicate, although in general still charac- 



