TEE NERVES. 701 



Ganglionic Nerves. — These nerves, collectively represent'ng the great 

 sympathetic system, form below and on the sides of the spine, two long cords, 

 rendered moniliform by the presence of ganglionic enlargements, and in 

 the constitution of which nearly all the cerebro-spinal nerves concur ; their 

 ramifications, frequently ganglionic also, are destined to the viscera of the 

 neck, the thorax, and the abdomen. 



In these nerves of organic life are found the two kinds of nerve-tubes, or 

 fibres of centripetal and centrifugal conductibility. 



But these tubes appear to have only very indirect relations with the 

 brain, for the will has no influence over the organs which receive their 

 nervous fibres from the great sympathetic ; and, besides this, in health, the 

 excitations developed in these organs are all reflected by the spinal cord, 

 and do not provoke in any way the special activity of the encephalon — they 

 are not felt. 



As the nerves of the great sympathetic system are principally formed of 

 fine tubes, we ought perhaps to seek in this anatomical condition the cause 

 of the special properties of these nerves ; what tends to make this appear 

 likely is the fact, that the cerebro-spinal nerves contain some of these 

 tubes in their elements, and that they share, with the ganglionic ramuscules, 

 the faculty of bringing into play the reflex power of the spinal cord. But 

 this is only a probability, and is unsupported by any direct proof. 



However this may be, it must be remarked that the special anatomical 

 and physiological characteristics of the sympathetic nerves should not cause 

 them to be considered as a system independent of the first, or cerebro-spinal 

 nerves. The fibres composing both have, in fact, a common origin in the 

 medullary axis, or rather those of the ganglionic nerves emanate from the 

 nerves of animal life. In the considerations which follow, we will therefore 

 omit this distinction of the nerves into two groups. 



Origin or the Nerves. — We ought to distinguish in these cords their 

 real or deep origin, and their superficial or apparent origin. The latter is 

 represented by the point of emergence of the roots of the nerves, which are 

 ordinarily spread in a fan shape, then united, generally after a very brief 

 course, into a single trunk, which offers at its commencement a ganglionic 

 enlargement, if fibres of general sensibility enter into its constitution. 

 Their real origin is the point of departure of these roots in the depth of 

 the cerebro-spinal axis. This is not well known, perhaps, of any nerve, even 

 of those whose radicles are easily followed into the substance of the nervous 



Distribution of Nerves. — The nervous trunks, formed by the radicles 

 of which we have just spoken, issue in pairs from the foramina at the base 

 of the cranium or in the walls of the spine, to be distributed to all parts of 

 the body by dividing into successively decreasing branches. Those among 

 these branches which ramify in the organs of animal life, generally follow 

 the track of the deep vessels or the subcutaneous veins, and are always 

 found most superficial. Their ramescence is effected in a very simple 

 manner, by the successive emission of the fasciculi composing the principal 

 trunks, until they are completely expended. These branches pursue their 

 course'nearly always in a direct line ; only some, as the ramifications of the 

 two principal nerves of the tongue, describe very marked fiexuosities, with 

 the same protective intention as the arteries of that organ. Anastomoses 

 sometimes join these branches to one another; and anastomoses, often 

 enough complicated, unite many nerves together, and form what are called 

 plexuses But in these anastomoses, no matter how complicated they may 



