3 68 TEXT-BOOK OF PHYSIOLOGY. 



skin of the head and face, to the blood-vessels of the skin of the upper and 

 lower extremities and trunk and to the blood-vessels of the thoracic and 

 abdominal viscera. 



The vaso-constrictors for the head and face emerge from the spinal 

 cord in the first four thoracic nerves, thence pass successively by way of the 

 white rami communicantes into and through the ganglion stellatum (the 

 first thoracic), the annulus of Vieussens, the inferior cervical ganglion, the 

 sympathetic cord to the superior cervical ganglion, around the cells of which 

 they arborize. From this ganglion the new fibers follow the carotid artery 

 and its branches to their terminations. 



The vaso-constrictors for the fore-limbs emerge from the cord in the roots 

 of the fourth to the tenth thoracic nerves inclusive. Through the white 

 rami they pass into the sympathetic chain, after which they take an upward 

 direction and terminate around the cells of the ganglion stellatum. From 

 this ganglion the new fibers enter, by way of the gray rami communicantes, 

 the trunks of the cervical nerves which unite to form the brachial plexus 

 and by this route pass to the blood-vessels of the skin and possibly of the 

 muscles of the fore-limb. 



The vaso-constrictors for the hind-limbs emerge from the cord in the 

 roots of the eleventh dorsal to the second or third lumbar nerves inclusive. 

 They then pass through the white rami to the lower lumbar and upper 

 sacral ganglia. Thence by way of the gray rami they pass into the nerve- 

 trunks which unite to form the sacral nerves and by this route pass to the 

 blood-vessels of the skin and possibly the muscles of the hind limb. 



The vaso-constrictors for the walls of the trunk of the body emerge 

 from the spinal cord between the second thoracic and third lumbar nerves. 

 They then pass by way of the white rami into the thoracic and lumbar 

 ganglia around the cells of which they arborize. From these ganglia new 

 fibers arise which pass by way of the gray rami into the thoracic and lum- 

 bar nerves and directly to the blood-vessels of the skin. 



The vaso-constrictors for the viscera of the abdominal cavity after 

 emerging from the spinal cord pass by way of the branches that unite to 

 form the splanchnic nerves directly into the collateral ganglia, the semilunar, 

 the superior mesenteric, the inferior mesenteric, and the sacral. From 

 these ganglia an elaborate network of non-medullated fibers passes to the 

 blood-vessels of the stomach, intestines, and other viscera. The great 

 splanchnic nerve is one of the most important vaso-constrictor trunks of the 

 body, on account of the large vascular area it controls. 



The existence, course, distribution, and functions of the vaso-constrictor 

 nerves have been determined by a variety of methods, physiologic and anat- 

 omic. Stimulation of the nerve-trunks under appropriate conditions 

 gives rise to a contraction, division to a dilatation of the blood-vessels. 

 The physiologic continuity of the pre-ganglionic fibers with the nerve-cells 

 of the sympathetic ganglia has been shown by the intra-vascular injection 

 or the local application of nicotin. This agent, as shown by Langley, has 

 a selective action on the arborizations of the pre-ganglionic fibers, and when 

 given in sufficient doses suspends their conductivity; hence stimulation of 

 pre-ganglionic fibers is without effect, though stimulation of the post- 

 ganglionic fibers is followed by the usual contraction. 



