THE NERVOUS SYSTEM. 653 



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/* instead 

 of 14. 4// to 19//. Such fibres are a peculiarity of the spinal nerve-roots 

 chiefly in the thoracic region, but they are also found in the second and 

 third 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 upward into the inferior 

 mesenteric ganglia and downward 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 communicat- 

 ing with the lateral ganglia; the branches which pass upward from the 

 thoracic region to the neck, he calls cervical splanchnics, and the 

 splanchnics proper abdominal splanclmics. The white rami viscerales of 

 the upper cervical and cervico-cranial regions do not run 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-pharyn- 

 geal 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 researches of Gaskell have, however, done much to 

 clear up the former confusion as to the functions of the sympathetic ; 

 and in the following account the description of the functions, as given 

 by that observer, is followed. 



The efferent nerve fibres of the sympathetic system supply (a) the 

 muscles of the vascular system, to which they send vaso-motor fibres, 

 i.e., vaso-constrictor and cardiac augmentor or accelerator, and vaso-in- 

 hibitory fibres, i.e., vaso-dilator and cardiac inhibitory; (b) the visceral 

 muscles, to which they send both viscero-motor and viscero-inhibitory 

 fibres, (c) The secretory gland-cells. 



(a) i. Vaso-motor or Vaso-constrictor and. Cardio-ougmentor Fibres. 

 The vaso-motor nerves for all parts of the body come from the central ner- 

 vous system, and pass out from the spinal cord in the white rami viscerales 

 of the thoracic region from the second thoracic to the second lumbar nerve- 

 roots inclusive, as fine medullated fibres; they then pass to the lateral or 

 main sympathetic chain, become non-medullated, and are distributed to 

 their muscles either directly or through terminal ganglia. Thus the aug- 



