668 TEXT-BOOK OF PHYSIOLOGY 



The functions of the thoracic fibers that terminate in the ganglia of the 

 same levels are (a) to augment the tonus and the degree of the contraction 

 of the blood-vessels of the skin of the arm and trunk of the body; and (b) to 

 augment the activities of the epithelium of the sweat-glands in the correspond- 

 ing regions. Stimulation of either the pre- or post-ganglionic fibers produces 

 the foregoing phenomena. 



The functions of the fibers that ascend the sympathetic chain to terminate 

 in the first thoracic, the inferior cervical ganglia are (a) to accelerate the rate 

 and the force of the contraction of the heart-muscle, and (b) perhaps augment 

 the activities of the epithelium of the thyroid gland. The pre-ganglionic- 

 fibers having these important functions emerge from the spinal cord for the 

 most part in the ventral roots of the second and third thoracic nerves. After 

 leaving these nerves by way of the rami communicantes they enter the thoracic 

 chain and pass upward to terminate in and around the cells of the inferior 

 cervical -ganglion in man and in the first thoracic ganglion in certain other 

 mammals. The post-ganglionic visceral fibers the cardiac nerves that 

 arise in the cells of these ganglia pass downward and forward and reach the 

 heart by way of the cardiac plexus. Stimulation of these nerves causes the 

 same effects in the heart as stimulation of the pre-ganglionic fibers in any 

 part of their course. The center of origin of these accelerator and aug- 

 mentor cardiac fibers has not been definitely located but there are reasons 

 for thinking it is in the medulla oblongata. 



The functions of the fibers which in their upward course form the cervical 

 cord and finally terminate around the nerve cells of the superior cervical 

 ganglion are: 



(a) To augment the tonus and increase the contraction of the blood- 

 vessels of the skin and mucous membrane of different portions of the head, 

 face and neck; (b) to augment the contraction of the blood-vessels of the sub- 

 maxillary, the sublingual and the parotid glands; and (c) to augment the activ- 

 ity of the epithelium of the sweat glands of the head, face and neck, and 

 possibly of the salivary glands as well, (e) To augment the tonus and the 

 contractions of the dilatator pupillos muscle, thus antagonizing and overcom- 

 ing the contraction of sphincter pupillos muscle and establishing a dilatation 

 of the pupil. 



The foregoing effects may be demonstrated by exposing and dividing 

 the cervical cord and then stimulating the peripheral end. The same phe- 

 nomena follow stimulation of the post-ganglionic branches. That the 

 superior cervical ganglion, like ganglia elsewhere in the body, is the cell 

 station between the spinal cord and the peripheral organs is shown by the 

 fact discovered and applied by Langley that the intra-venous injection of 

 nicotin or the local application of it to the ganglion itself, impairs the con- 

 ductivity of the terminals of pre-ganglionic fibers, after which their stimula- 

 tion has no effect on the ganglion cells, though the latter retain their activity, 

 as shown on direct stimulation. 



The functions of the fibers that cross the sympathetic chain and unite 

 to form the greater and lesser splanchnic nerves together with their ganglionic 

 continuations (semilunar ganglion and the fibers of the solar plexus) are: 

 (a) To augment the tonus and contractile power of the walls of the blood- 

 vessels of the stomach and intestines as far as the descending colon (the so- 

 called splanchnic vascular area) and the blood-vessels of the kidney and 



