WORK UPON VISCERAL AND ALLIED NERVES. 39 



cat as presenting sev^eral variations. These he divides into 

 three chief groups called respectively anterior, median, and 

 posterior. " The simplest method of distinguishing these 

 classes is to note the relative size of the strands to the 

 sciatic furnished respectively by the sixth lumbar and by 

 the upper branch of the first sacral. If the former is 

 distinctly larger than the latter, the plexus belongs to the 

 anterior class ; if the two are of about the same size, the 

 plexus is median ; if the strand from the first sacral is dis- 

 tinctly larger than that from the sixth lumbar, the plexus is 

 of the posterior class." 



VASO-MOTOR NERVES. 



Gaskell,^ in his important paper upon visceral and 

 vascular nerves, deals with the question of the course 

 and distribution of the two sets of vaso-motor nerves. 

 The method he employed was to a large extent an 

 anatomical one. He showed that the visceral fibres present 

 in any root may all be traced into the white ramus com- 

 municans of that root, because their transverse diameter is 

 much smaller than the average diameter of the ordinary 

 sensory and motor fibres of the two roots. He concludes 

 that vaso-constrictor nerves for all parts of the body are re- 

 stricted to the anterior roots of the spinal nerves between 

 the second thoracic and fourth lumbar inclusive, whence 

 they pass as medullated nerves to the ganglia of the main 

 sympathetic chain, from which they issue as non-medullated 

 nerves and pass to their destination. For vaso-dilator 

 nerves, he shows that some leave by the cervico-cranial and 

 sacral sets of visceral nerves ; but whether there are more 

 from other roots he does not decide. 



To the Trunk and Livibs. — By recording plethysmo- 

 graphically the variations in volume of the limbs and the 

 general blood pressure simultaneously, Bradford and Bayliss^ 

 have examined the origin of the constrictor nerves to the 

 limbs. For the fore-limb in the dog, they find constrictor 



'^ Journ. of Physiol., vol. vii., p. i, 1885-6. 

 "^ Ibid., vol. xvi., p. 10, 1894. 



