PLEXUSES. 325 



thin transverse section of a branch of a ganglionic nerve ex- 



Slice of a branch of a ganglionic nerve. (M. Raspail.) 

 hibits a single chord ; but a similar section of the median of the 

 arm exhibits several, every chord having its own membrane, as 



Slice of the median nerve of the arm : 

 the cut ends of the fibrils are seen, with 

 the covering of every bundle, and of the 

 whole. The single spot represents a 

 blood-vessel. (M. Raspail.) 



well as the whole one in common ; and their number is greater, 

 the further from the head the examination is made. 



A longitudinal view presented the filaments with a granulated 

 appearance, like the orifices of tubes ; but this was probably the 

 effect of the refraction of light, and it occurred when other 

 textures were examined in the same way. (See first cut over- 

 leaf.) Each cylinder of a human nerve is said by M. Raspail to 

 be about '00787 of an inch in diameter. 



Though the fibres are parallel, their filaments continually unite, 

 so that a nerve appears more or less reticular. 



A plexus is the same arrangement on a large scale. n 



Ganglions consist, like the encephalon and spinal chord, and 



m Professor Ehrenberg says that the olfactory and optic nerves, and the branches 

 of the sympathetic, are entirely composed of granulated or knotted fibres ; while 

 nerves of motion and the regular spinal nerves are cylindrical and tubular, and 

 continuations of knotted fibres of the brain now become cylindrical. 



n Dr. Macartney asserts, indeed, that in all plexuses a complete mingling of 

 the substance of all the nerves takes place, and that there no less is a mingling 

 of the roots of the spinal nerves with the spinal chord. (1. c. p. 451.) 



z 4 



