MOVEMENTS OF THE ALIMENTARY CANAL, ETC. 385 



small intestine and the greater part of the large intestine receive visceromotor 

 nerve-fibres from the vagi and the sympathetic chain. The former, according 

 to most observers, when artificially stimulated cause movements of the intestine, 

 and are therefore regarded as the motor fibres. It seems probable, however, 

 that the vagi carry or may carry in some animals inhibitory fibres as well, and that 

 the motor effects usually obtained upon stimulation aredue to the fad that in these 

 nerves the motor fibres predominate. The fibres received from the sympathetic 

 chain, on the other hand, give mainly an inhibitory effect when stimulated, 

 although some motor fibres apparently may take this path. Bechterew and 

 Mislawski 1 state that the sympathetic fibres for the small intestine emerge from 

 the spinal cord as medullated fibres in the sixth dorsal to the first lumbar 

 spinal nerves, and pass to the sympathetic chain in the splanchnic nerves and 

 thence to the semilunar plexus, while the sympathetic fibres to the large intes- 

 tine and rectum arise in the four lower lumbar and the three upper sacral spinal 

 nerves. According to Langley and Anderson 2 the descending colon and rec- 

 tum receive a double nerve-supply — first from the lumbar spinal nerves (second 

 to fifth), the fibres passing through the sympathetic ganglia and the inferior 

 mesenteric plexus and causing chiefly an inhibition ; second, through the sacral 

 nerves, the fibres passing through the nervus erigens and the hypogastric plexus 

 and causing chiefly contraction of the circular muscle. 



These extrinsic fibres undoubtedly serve for the regulation of the move- 

 ments of the bowels from the central nervous system ; conditions which influ- 

 ence the central system, either directly or indirectly, may thus affect the intesti- 

 nal movements. The paths of these fibres through the central nervous system 

 are not known, but there are evidently connections extending to the higher 

 brain-centres, since psychical states are known to influence the movements of the 

 intestine, and according to some observers stimulation of portions of the cere- 

 bral cortex may produce movements or relaxation of the walls of the small and 

 large intestines. As in the case of the stomach, the extrinsic fibres seem to 

 have only a regulatory influence. When they are completely severed the 

 tonicity of the walls of the intestine is not altered, and peristaltic and rhythmic 

 movements still occur. The same results may be obtained even upon ex- 

 cised portions of the intestines (Salvioli, Mall). It seems probable, there- 

 fore, that normal peristalsis in the living animal may be effected independently 

 of the central nervous system, although its character and strength is subject 

 to regulation through the medium of the viscero-motor fibres, in much the 

 same way, and possibly t<> as great an extent, as the movements of the heart are 

 controlled through its extrinsic nerves. 



Effect of Various Conditions upon the Intestinal Movements. — Experi- 

 ments have shown that the movements of the intestines may be evoked in many 

 ways beside direct stimulation of the extrinsic nerves. Chemical stimuli may 

 be applied directly to the intestinal wall. Mechanical stimulation, pinching, 

 for example, or the introduction of a bolus into the intestinal cavity, will 



1 Du Bois-Reymond' a Archiv fur Physiologic, 1889, Suppl. Bd. 

 1 Journal of Physiology, 1895, vol. xviii. p. 67. 



Vol.. I.— 25 



