206 



ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 



sions, and that the ganglion itself receives these impressions, and makes them 

 felt as sensations. On the other hand, if the separated portion of the trunk 

 be irritated, motions are excited in the muscles which it supplies ; showing 

 that it is still capable of conveying the motor influence, though cut oft" from 

 the usual source of that influence. 



242. In the ordinary Nerve-trunks, we find only one form of Nervous tis- 

 sue; that which may be designated as the fibrous or tubular. In the Gan- 

 glia, we find, in addition to this, a substance made up of peculiar cells or 

 vesicles ; which may be distinguished as the vesicular nervous matter. In 

 fact, the character of a Ganglionic centre (which is frequently not otherwise 

 clearly distinguished as such) is derived from the presence of this vesicular 

 substance. 



243. The ultimate Nerve-fibre, in its most complete form, such as is pre- 

 sented to us in the ordinary spinal nerves, is distinctly tubular ; being com- 

 posed of an external cylindrical membranous sheath, within which the peculiar 

 nervous matter is contained. This membranous tube, like the Myolemma of 

 muscular fibre, is extremely delicate and transparent ; and is nearly or quite 



c 6 c d 



A. Diagram of tubular fibre of a spinal nerve ; a. Axis cylinder. 6. Inner border of white substance, 

 c, c. Outer border of white substance, d, d. Tubular membrane. B. Tubular fibres ; e, in a natural 

 slate, showing the parts as in A. f. The white substance and axis cylinder interrupted by pressure, 

 while tin; tubular membrane remains, g. The same, with varicosities. h. Various appearances of the 

 wliite substance and axis cylinder forced out of the tubular membrane by pressure. ('. Broken end of a 

 tubular fibre, with the white substance closed over it. k. Lateral bulging of wliite substance and axis 

 cylinder, from pressure. I. The same more complete, g'. Varicose fibres of various si/.es, from the 

 cerebellum, r. Gelatinous fibres from the solar plexus, treated with acetic acid, to exhibit their cell- 

 nuclei. B and c magnified 320 diameters.] 



homogeneous. It is not penetrated by blood-vessels ; nor is it ever seen to 

 branch or anastomose with others ; so that there is reason to regard it as form- 



