THE SYMPATHETIC NERVE SYSTEM. 617 



are excited to activity emerge from the cord by the first and second 

 thoracic nerves. Stimulation of the white rami of these nerves gives 

 rise to the same results. 



(b) The splanchnic nerves, the roots of which emerge from the fourth to the 

 tenth or eleventh thoracic ganglia. The fibers composing these nerves 

 are for the most part pre-ganglionic and derived from the corresponding 

 spinal nerves. The cell stations of the splanchnic fibers are in the 

 semilunar, superior mesenteric, and renal ganglia. From these ganglia 

 non-medullated post-ganglionic fibers pass peripherally to the walls of 

 the intestines, the blood-vessels of the intestines, liver, kidneys, spleen, 

 etc. Stimulation of the great splanchnic produces inhibition of the 

 gastric and intestinal movements and a loss of tone, though occasionally 

 there is a slight opposite effect, namely an augmentation of the move- 

 ments, a marked primary contraction of the intestinal blood-vessels and 

 other viscera, followed by dilatation, coincidently with which there is a 

 primary rise succeeded by a fall of blood-pressure throughout the body. 

 Division of the nerve is followed by dilatation of the intestinal vessels 

 and a fall of blood-pressure. Stimulation of the central end of the divided 

 nerve excites the activity of the general vaso-motor center, as shown 

 by the rise of the general blood-pressure. Stimulation of the smaller 

 splanchnics gives rise to a slight primary contraction of the blood-vessels, 

 soon followed by a marked dilatation. These facts indicate that the 

 splanchnic nerves contain visceral nerves which inhibit and at times 

 augment intestinal movements, vaso-motor fibers both augmentor and 

 inhibitor, secretor nerves for the intestinal glands and for the adrenal 

 glands. 



(c) The cutaneous nerves for the trunk leave the lateral ganglia by the gray 



rami, enter the thoracic spinal nerves, and pass in company with them 

 to their terminations, to be ultimately distributed to the walls of the 

 blood-vessels, the arrectores pilorum muscles, and the sweat-glands. 

 The pre-ganglionic fibers come from the spinal nerves by way of the 

 white rami. Stimulation of either the white or gray rami gives rise to 

 contraction of blood-vessels, erection of hairs and a secretion of sweat. 

 Their functions are therefore vaso-motor, pilo-motor, and secreto-motor. 



(d) The cutaneous nerves for the fore-limbs have their origin from cells 

 in the stellate ganglion (first dorsal). After a short upward course they 

 enter the trunks of the nerve composing the brachial plexus. The 

 pre-ganglionic fibers come from the white rami of the fourth to the 

 ninth thoracic nerves. After entering the lateral chain they take an 

 upward direction and arborize around the cells of the stellate ganglion. 

 In the brachial and in the sciatic nerves as well vaso-motor fibers (con- 

 strictors and dilatators) and secretor fibers are present, as shown by 

 experimental methods (see page 488). 



The Functions of the Lumbo-sacral Portion. In the lumbar region 

 the vertebral chain contains a number of pre-ganglionic fibers which have 

 descended from the thoracic region, as well as fibers which have come into 

 the chain by the white rami from the lumbar nerves themselves. Some of 

 these fibers pass through the chain in a manner similar to the splanchnic 

 nerves in the thoracic region to reach the inferior mesenteric ganglion, in 



