CHAP, i.] TISSUES AND MECHANISMS OF DIGESTION. 467 



Indeed we may perhaps call the vagus fibres which pass to the 

 stomach and intestines (and these we may remark are, like the 

 cardiac augmentor fibres, non-medullated fibres along the greater 

 part of their course) augmentor fibres rather than motor fibres. 

 We have all the more reason to do so since there exist companion 

 but antagonistic inhibitory fibres. If while lively peristaltic 

 action is going on in the bowels, the splanchnic nerves be 

 stimulated the bowels are brought to rest, often in a very abrupt 

 and marked manner. Inhibitory fibres therefore run in the 

 splanchnic nerves, Fig. 70, Spl maj. and min., passing along them 

 from the spinal cord to the abdominal plexuses, and thence to 

 the alimentary canal ; probably some of the fine medullated fibres 

 which may be observed along this track are of this nature. 



It will be noticed that the splanchnic nerves while containing 

 vaso-constrictor i.e. augmentor fibres for the blood vessels of the 

 intestines, carry inhibitory fibres for the muscular coat ; and 

 probably the vagus while containing augmentor fibres for the 

 muscular coat carries inhibitory dilator fibres for the blood vessels. 

 It may further be remarked that the vagus while supplying aug- 

 mentor fibres for the muscular mechanisms of the alimentary canal 

 carries, as we so well know, inhibitory fibres for the cardiac 

 muscular mechanism. 



In the above statement we have purposely used the general 

 term peristaltic movement, but as we have seen, in the movements 

 of the alimentary canal, two sets of muscles are concerned, the 

 circular and the longitudinal. Now in the rectum we are able to 

 recognise that the two sets of muscles have quite distinct nervous 

 supplies. The longitudinal coat is governed by nerve-fibres which, 

 in the dog, leave the spinal cord in the anterior roots of the 

 second and third sacral nerves, Fig. 70, 82, S3, pass along the 

 branches of those nerves, frequently spoken of as the nervi eri- 

 gentes, I. r., to the hypogastric plexus, pi. hyp., and thence to the 

 rectum. Stimulation of these nerves causes contractions of the 

 rectum which are confined to the longitudinal coat and as we 

 have said pull the rectum down. The circular coat is governed 

 by fibres which leave the spinal cord by the anterior roots of 

 the lower dorsal and first two lumbar nerves, Fig. 70 (coming 

 from the lower part of that spinal region from which as we have 

 seen 169 the vaso-constrictor fibres take origin), and, early losing 

 their medulla, pass to the rectum by the inferior mesenteric 

 ganglia, the hypogastric nerves and hypogastric plexus, Fig. 70, 

 m. gl., n. hyp. pi., hyp. Stimulation of these fibres gives rise to con- 

 tractions which are confined to the circular coat, and squeeze out 

 the contents of the rectum. A similar double nervous supply 

 probably governs the longitudinal and circular coats along the 

 whole alimentary canal; but the details of such a supply are at 

 present unknown. 



Our knowledge moreover concerning the details of any special 



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