WORK UPON VISCERAL AND ALLIED NERVES. 57 



anterior and posterior roots of the sixth and seventh spinal 

 nerves. He obtains reflex contractions from stimulation 

 of the posterior roots of one side after section of all the 

 anterior roots on both sides, and of the posterior on the 

 side stimulated. 



T/ie anus. — Sherrington, ^ when making observations 

 on the fibres of the anterior roots forming the lumbo-sacral 

 plexus, describes that when all the anterior roots of this 

 reeion were cut the anus remained closed but less retracted 

 than usual. On being opened by a sound it remained 

 open after the sound was removed, but that on stimulation 

 of some of these roots the anus being open, it was smartly 

 closed by a contraction of the sphincter muscle. The roots 

 which were effective in the cat were the eighth and ninth 

 post-thoracic, sometimes the seventh. In Macacus, the 

 root was the eighth, and either the seventh or ninth, though 

 always to a less extent. When one root remained intact 

 it did not remain patulous, and no asymmetry was pro- 

 duced by section of all three roots on one side. On 

 excitation of a root when the anus was patulous a sym- 

 metical contraction was obtained if the stimulus was strong, 

 if weak sometimes an asymmetrical contraction was pro- 

 duced. Langley and Anderson ^ describe the upper set of 

 fibres to contain in a rabbit inhibitory fibres for the in- 

 ternal sphincter, and obtained some evidence which, how- 

 ever, they did not consider very satisfactory, of motor fibres. 

 In addition these fibres contained motor fibres for the non- 

 striated muscles beneath the skin in the neighbourhood of 

 the anus. These fibres chiefiy innervated the half of the 

 corresponding side. The origin from the cord was rather 

 more restricted than for those fibres which innervated the 

 colon and rectum. In the cat this set, on stimulation caused 

 marked contraction of the internal sphincter. Stimulation 

 of the sacral set of fibres in the rabbit caused dilatation of 

 the internal sphincter ani which was usually followed one or 

 two seconds after cessation of the stimulus by a marked 

 contraction. There are thus motor fibres for this muscle 



'^Journ. of Phys., vol. xiii., p. 672, 1892. 

 - Loc. cit. 



