200 THE NERVOUS SYSTEM. 



throug-h the Bavri communicantes with the sympathetic gaiigha (ver- 

 tebral or lateral ganglia) ; these two sets of ganglia Gaskell terms 

 proximal. By means of the branches from the sympathetic ganglia 

 [Rami efferentes) part of the fibres pass to another set of ganglia, the 

 solar plexus, etc., which he terms prevertebral or collateral ; from 

 these the fibres pass to be distributed to the various viscera and blood- 

 vessels, where a fovirth set of very small ganglia (terminal ganglia) 

 is found. The prevertebral and terminal ganglia are together classed 

 as distal ganglia. Gaskell holds that the fine medullated fibres 

 from the cord lose their medullary sheath in one or other of these 

 ganglia according to the function they fulfil. 



The inhibitory fibres of the heart and vaso-dilator fibres of the 

 blood-vessels continue as white fibres along the vago-symj^athetic and 

 spinal nerves to the distal ganglia (Bidder^s ganglion, etc.), where 

 the medullary sheath disappears: whereas the 'augmentor^ fibres of 

 the heart and vaso-constrictor fibres of the blood-vessels lose their 

 medullary sheath in the proximal ganglia and pass on as non- 

 medullated fibres. In the same w^ay the nerve-fibres that bring 

 about contraction of the circular muscle fibres of the hollow viscera 

 lose their medullary sheaths in the proximal ganglia, while those 

 fibres, the influence of which negatives the former, become pale 

 fibres in the distal ganglia. 



Waters has demonstrated that in the frog the various spinal 

 nerves have each a localised physiological action upon the blood- 

 vessels and muscular walls of various parts of the alimentary canal : 

 he shows that 



The third spinal nerve supplies the oesophagus. 



The fourth spinal nerve supplies the stomach. 



The fifth spinal nerve supplies the upper third of the small 

 intestine. 



The sixth spinal nerve supplies the lower two thirds of the small 

 intestine. 



The seventh spinal nerve supplies the large intestine. 



The eighth spinal nerve supplies the bladder, this supply being, 

 however, not so definite as the others given above. 



It has long' been known that the branches of the spinal ganglia 

 (ganglia of the posterior roots) are together larger (one-third, 

 Lenhossek), and contain more fibres than the ventral and dorsal 

 roots together ; this is supposed to be in part due to an acquisition 

 of new fibres derived from the ganglia. The majority of recent 

 observers hold that each ganglionic cell has only one process, which. 



