5 68 TEXT-BOOK OF PHYSIOLOGY. 



The Functions of the Thoracic Portion. The phenomena 

 which follow stimulation of this portion of the sympathetic system 

 resemble in a general way those observed in the head when the cervical 

 portion is stimulated. The situation of the resulting phenomena 

 will vary in accordance with the part the subject of the experiment. 

 For an understanding of the results of experiment the origin and 

 distribution of the following nerve-branches must be kept in view : 



(a) The cardiac nerves which have their origin in the first thoracic 

 ganglion. From this point they pass by way of the annulus of 

 Vieussens to the inferior cervical ganglion (from which they 

 probably receive additional fibers) and thence to the heart. 

 Stimulation of these nerves gives rise to an increased frequency 

 and an augmentation in the force of the heart-beat. The pre- 

 ganglionic fibers by which these cells are excited to activity 

 emerge from the cord by the first and second thoracic nerves. 



(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-gang- 

 lionic 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 

 intestinal movements, 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 intestinal movements, vaso-motor fibers both aug- 

 mentor and inhibitor. The presence of secretory nerves for 

 the intestinal glands is disputed. 



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



the gray rami, enter the thoracic spinal nerves, and pass in com- 

 pany with them to their terminations, to be ultimately distrib- 

 uted 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 the white rami. Their functions are 

 vaso-motor, pilo-motor, and secretor. The cutaneous nerves 



