THE SPINAL NERVES 



6l 



to the rest of the body. But GaskeU (1886) was the first to make a detailed 

 study of the nerve-fibers supplying the visceral and vascular systems. We 

 now recognize in the spinal nerves elements belonging to four functionally 

 distinct varieties, namely, visceral afferent, visceral efferent, somatic afferent, and 

 somatic efferent fibers (Fig. 37). 



Visceral Components. The fibers which innervate the visceral and vascular 

 systems, including all involuntary muscle and glandular tissue, possess, as 

 Gaskell (1886) pointed out many years ago, certain distinguishing character- 

 istics. They are all fine myelinated fibers and end in sympathetic ganglia 



Somatic afferent fiber \ Dorsal root 

 Visceral afferent fiber) 



Spinal ganglion 

 Dorsal ramus 



f Ventral ramus 



| 



" Ramus communicans 



Sympathetic ganglion 



/*. Visceral efferent fiber], , . , 

 S Somatic efferent fiber Central root 



Postganglionk fiber 



,Viscus 



Fig. 37. Diagrammatic section through a spinal nerve and the spinal cord in the thoracic region 

 to illustrate the chief functional types of peripheral nerve-fibers. 



from which the impulses are relayed to involuntary muscles and glands by a 

 second set of neurons (Fig. 37). They are usually designated as visceral efferent 

 fibers, and they run by way of the white rami to the sympathetic ganglia. It 

 is usually stated that they are found only hi the second thoracic to the second 

 lumbar nerves inclusive, but Langley (1892) has shown that in the cat, dog, 

 and rabbit they are present in all the thoracic and the first four lumbar nerves, 

 and Miiller (1909) found white rami associated with the third and fourth lumbar 

 nerves in man. 



There are also visceral afferent fibers distributed to the thoracic and ab- 

 dominal viscera by way of the white rami from the thoracic and upper lumbar 



