THE SYMPATHETIC AND PARASYMPATHETIC SYSTEMS 629 



A. The sympathetic chain, situated on each side of the vertebral column and con- 

 sisting of ganglia which are connected by strands of fibers. It is divided into a : 

 (a) Cervical portion which is placed along the neck and is beset with the superior, 



middle and inferior cervical ganglia. This delicate string of non-medullated 

 fibers may pursue an independent course along the carotid artery (rabbit) 

 or be intermingled with the medullated fibers of the vagus (dog). 

 (6) Thoracic portion, consisting of eleven or twelve ganglia, the first three of 

 which are united into the large ganglion stellatum. 



(c) Lumbar portion, embracing the three or four ganglia of this region. 



(d) Sacrococcygeal portion, formed by an equal number of sacral gangUa 

 terminating with the ganglion coccygeum. 



B. A system of large ganglia which may be grouped as : 



(a) Cranial, for example, the ganglion ciliare upon the third nerve, the gangUon 

 sphenopalatinum upon the second branch of the trigeminus, the ganglion 

 oticum et ganglion submaxillare upon the third branch of the same nerve. 

 The vagus and glossopharyngeus also embrace certain fibers which connect 

 with the sympathetic system. 



(6) Thoracic, for example, the plexus cardiacus upon the arch of the aorta. 



(c) Abdominal, for example, the plexus Solaris, embracing the right and left 

 suprarenal, the superior mesenteric, the celiac and certain smaller gangHa in 

 the region of the stomach. The greater and lesser splanchnic nerves unite 

 this complex with the thoracic ganglia. The distalmost ramifications of the 

 sympathetic system in this region form the plexuses of Meissner and Auerbach. 



(d) Pelvic, for example, the ganglion hypogastricum. 



Characteristics of the Autonomic Nervous System. — The preceding 

 outline teaches us that the autonomic nervous system occupies an 

 anatomically distinct position; in fact, its gross anatomical charac- 

 teristics are such that we are tempted to regard it as a nervous system 

 within a nervous system. On the histological side, we find that the 

 sympathetic cells are usually multipolar, rounded in outline, and some- 

 what smaller than those belonging to the cerebrospinal structures. 

 The nerve-fibers are characterized by an absence of the myelin sheath 

 which imparts to them a grayish color. The only exception to this 

 rule is to be found in the medullated fibers, forming the connection 

 between the gray matter of the cerebrospinal system and the neighbor- 

 ing sympathetic ganglia. These bridges of fibers are known as the 

 white rami communicantes. On the physiological side, we observe 

 that the reactions occurring in the realm of the sympathetic system, 

 are for the most part subconscious. This implies that they are not 

 under the direct guidance of volition and are, therefore, typically 

 reflex in their character. Besides, as they are relatively independent 

 of the central nervous system, and may continue even after the de- 

 struction of the latter, they are usually described as autonomic. . On 

 the pharmacological side, we find that the sympathetic elements behave 

 in a very characteristic manner toward certain drugs. Nicotin acts 

 as a cell poison, i.e., it paralyzes the synapses and thus separates the 

 distal from the central neuron. Efferent impulses are in this way 

 prevented from reaching the peripheral motor organ. Adrenalin 

 exerts a specific action upon the thoracic and lumbar divisions of the 

 sympathetic system, while atropin, muscarin and pilocarpin are said 



