ORIGIN OF GREY RAMI FROM GANGLIA. 629 



extent; they encroach very little on their neighbour's territory. We 

 must conclude, then, that although the efferent sympathetic fibres 

 accompany the sensory spinal fibres to the skin, they spread out less in 

 the skin than do the sensory fibres. Thus the efferent sympathetic 

 nerve region lies in the afferent spinal nerve region. 



Turning now to the distribution of the grey rami which run to the 

 limbs, we have no pilo-motor fibres to serve as indicators, and although 

 the vasomotor fibres afford some aid, we have for accurate observations 

 on distribution to rely upon the sweat glands in the pads of the cat's 

 foot. 1 As a rule, four grey rami send secretory nerves to the foot of 

 the cat, namely, the sixth lumbar to the second sacral ; the second sacral 

 grey ramus occasionally has no effect. In a typical case the sixth 

 lumbar grey ramus causes secretion in the inner part of the foot, the 

 second sacral grey ramus causes secretion on the outer part of the foot, 

 the other two cause copious secretion on the whole of the foot, but the 

 seventh lumbar most on the inner part, and the first sacral most on the 

 outer part. Here, then, each part of the skin receives fibres from three 

 grey rami. Some parts, in some cases, receive fibres from four grey 

 rami. Tiirck * 2 and Sherrington 3 have shown that the afferent fibres of 

 the nerves which go to make up the sciatic, overlap very largely. The 

 overlapping described by them is, however, hardly so great as that which 

 occurs in the secretory fibres of the several grey rami. In the limbs, 

 then, unlike the trunk, the sympathetic efferent areas of the grey rami 

 appear to overlap rather more than do the afferent skin fibres of the 

 corresponding spinal nerves'. 



Origin of grey rami from the ganglia. — Having thus determined 

 the course taken by sympathetic fibres, on passing from the sympathetic 

 chain to the skin, our next step is to determine from what nerve cells 

 the nerve fibres arise. This can be done by the use of nicotin, in the 

 manner already given in treating of the cervical sympathetic. The result 

 of such experiments is, that the great majority of the fibres of a grey 

 ramus, in some cases all of them, arise from the corresponding vertebral 

 sympathetic ganglion, and run to the periphery without having further 

 sympathetic nerve cells on their course. The few fibres which do not 

 arise from the corresponding ganglion arise from the ganglion next 

 above or below, and in the case of the lumbar grey rami from the 

 ganglion next above ; in the case of the thoracic . and sacral ganglia 

 there appears to be some variation, but the details have not been fully 

 worked out. 



Broadly speaking, then, the vertebral sympathetic ganglia are seg- 

 mental, and each supplies sympathetic fibres to its own spinal nerve. 



There is a divergence from this rule, though functionally not a very 

 important one ; the white rami not infrequently receive a few fibres 

 from the sympathetic ganglia. Where the white rami run posteriorly 

 before joining the sympathetic chain, as they do in the cat, from the 

 tenth or eleventh thoracic to the fourth or fifth lumbar, a white ramus 

 may receive fibres from the nerve cells of the ganglion of the nerve 

 immediately posterior to it (cf. Fig. 309). 



1 Langley, Journ. Physio/., Cambridge and London, 1891, vol. xii. p. 368; 1894, vol. 

 xvii. p. 299. 



2 Sitzungsb. d. k. Akad. d. Wisscnsch., Wien, 1856, Bd. xxi. S. 586; Denkschriften d. 

 k. Akad. d. Wissensch., Math.-JVat. CI., Wien, 1869, Bd. xxix. S. 299. 



3 Phil. Trans., London, 1893, vol. clxxxiv. p. 641. 



