THE SYMPATHETIC NERVOUS SYSTEM. 627 



nerves are the only apparent representatives of the visceral branches in 

 the regions above the 2d thoracic nerve root, and below the 2d lumbar 

 nerve root, with the exception of the roots of the 2d and 3d sacral 

 nerves, which have also white rami, and consist of non-medullated fibres 

 and pass from the ganglia to be distributed chiefly to the spinal column, 

 to the spinal membranes and to the spinal nerve roots themselves. "We 

 must look upon the white rami then as the visceral branches proper. 



A peculiarity in the structure of these white medullated visceral 

 nerves is the fineness of their fibres. They are a third or a fourth of the 

 diameter of ordinary medullated fibres, measuring 1.8/< to 2.7>w instead 

 of 14.4yw to 19yU. They are a peculiarity of the spinal nerve roots chiefly 

 in the thoracic region, but are also to be found in the 3d and 3d sacral 

 nerves, and constitute there the nervi erigentes which pass directly to 

 the hypogastric plexus, and not first of all into the lateral chain. From 

 this plexus branches pass upwards into the inferior mesenteric ganglia 

 and downwards to the bladder, rectum and generative organs. These 

 nerves, called by Gaskell pelvic splanchnic nerves, differ from the rami 

 viscerales of the thoracic region only in not communicating with the 

 lateral ganglia; the branches which pass upwards from the thoracic re- 

 gion to the neck, he calls cervical splanchnics, and the splanchnics 

 proper abdominal splanchnics. The white rami viscerales of the upper 

 cervical and cervico-cranial regions do not rim with their corresponding 

 gray rami, but form, Gaskell thinks, the internal branch of the spinal 

 accessory nerve, which contains small medullated fibres similar to those 

 of the visceral branches in the thoracic region. This branch passes 

 into the ganglion of the trunk of the vagus. Small visceral fibres exist 

 too in the roots of the vagus, and in those of the glosso-pharyngeal in 

 connection with the ganglion of the trunk and ganglion petrosum, as 

 well as in the -chorda tympani, in the small petrosal and in other cranial 

 visceral nerves. 



Functions. The functions of the sympathetic system are not by any 

 means completely understood. Indeed, until within the last few years, 

 what could be said about them was of a very vague kind. The remarka- 

 ble researches of Gaskell 'have, however, done much to clear up the 

 former confusion; and in the following account the description of the 

 functions of the sympathetic as given by that observer, will be to a great 

 extent followed. 



A. Functions of the nerve fibres. The efferent nerve fibres of 

 the sympathetic system supply (a) the muscles of the vascular sys- 

 tem, to which they send vaso-motor fibres, i. e., vaso-constrictor and 

 cardiac augmentor or accelerator, and vaso-inhibitory fibres, i. e., vaso- 

 dilator and cardiac inhibitory; (b) the muscles of the viscera, to which 

 they send both viscero-motor and viscero-inhilitory fibres, (c) The se- 

 cretory gland-cells. 



