THE CIRCULATION THROUGH THE LIMBS. 



157 



The chief outtiow of constrictor fibres occurs from the sixth dorsal to 

 the first lumbar nerve. Thus the limbs and the abdominal viscera get 

 their supply approximately from the same part of the spinal cord. The 

 vasomotor mechanism of the limbs is not powerfully developed. 



By stimulation of any sensory nerve the vessels of the limbs can be 

 constricted. Usually, however, the limbs expand owing to the passive 



Fir, 97. — Effect of excitation of a superficial branch of the crural nerve on the arterial 

 pressure, and on the volume of the spleen, jejunum, kidney, and feet. — Hallion and 

 Francois- Fran ck. 



dilatation produced by the rise of aortic pressure which follows reflex 

 constriction of the splanchnic vessels. The reflex constriction of the 

 limbs can be obtained after section of the splanchnic nerves. 



Langley's 1 observations on the vaso-constrictor fibres of the feet 

 agree closely with those of Bayliss and Bradford. He further finds that 

 the sympathetic cell stations for the fibres of the upper limb are in 

 the stellate ganglion ; of the hind-limb, in the sixth and seventh lumbar 

 and first sacral ganglia. The vasomotor fibres to the trunk follow 

 the same distribution as the pilomotor fibres. 



The general changes which take place on exciting the central end of an 

 afferent nerve are seen exceedingly Avell in Fig. 97. In this there is shown 

 a simultaneous record of — 



1 Jmtrv. Physiol., Cambridge and London, 189], vol. xvi. p. 375 : 1894-5, vol. xvii. p. 307. 



