638 SYMPATHETIC AND OTHER SYSTEMS OF NERVES. 



cases one or two degenerated fibres were found ; these could be referred either 

 to an implication of the spinal ganglion in the injury, or to fibres passing to the 

 grey ramus from the white ramus of one of the cut nerves. 



Limits of white rami in different mammals. — Of the cat we 

 have already spoken. With regard to the white rami in other animals, 

 our knowledge is less accurate than could be wished ; but there is more 

 or less evidence for the following statements. The first thoracic nerve 

 is in all animals the first nerve to give off a white ramus. Eelatively, 

 as well as absolutely, there are fewer fibres in the first thoracic white 

 ramus of the rabbit than in that of the cat, dog, monkey, and man. 

 In the dog the last white ramus comes from the third lumbar nerve, 

 with anterior arrangement of nerves, otherwise from the fourth. In 

 the rabbit, the last nerve with a white ramus is the fourth or fifth. 

 In man, it is, so far as is known, the second lumbar ; 1 whether the 

 second lumbar nerve has always a white ramus, and whether the third 

 lumbar nerve has a white ramus when the arrangement of nerves is 

 markedly posterior, has not been sufficiently investigated. 



Course of post-ganglionic sympathetic fibres to the skin.— 

 On reviewing the course of the sympathetic efferent fibres to the skin, 

 we see that the peripheral fibres all arise from the ganglia of the sympa- 

 thetic chain. The post-ganglionic fibres, almost without exception, pass 

 by grey rami to the cerebro-spinal nerves, and accompany the cutane- 

 ous branches of these nerves. And, further, the fibres of each grey 

 ramus have in the main the same distribution in the skin, as the afferent 

 cerebro-spinal fibres of the nerve it accompanies. 



General scheme of the connections of the white rami with the 

 vertebral ganglia.— A consideration of the connections of the several 

 spinal nerves given above, shows that they are arranged with a 

 certain symmetry (cf. especially table, p. 634). Each spinal nerve, from 

 the first thoracic to the fourth lumbar (cat, anterior arrangement), sends 

 fibres to a series of ganglia, varying usually from six to nine, and in no 

 case to a single segmental ganglion. Each spinal nerve sends its rays 

 of fibres a little more anteriorly than the spinal nerve behind it, and a 

 little more posteriorly than the one in front of it. Thus, speaking 

 broadly, the successive spinal nerves give off sympathetic fibres to 

 successive largely overlapping portions of the skin of the body. 



Although each spinal nerve sends fibres to a series of ganglia, it does not 

 send an equal number to each of them. In each case it sends more fibres to 

 one or two ganglia than to any others ; and from this position of maximum 

 supply there is a regular diminution in the number of fibres sent to the 

 several ganglia of the series. The position of maximum supply is not 

 necessarily, or even usually, in the middle of the series, but it would take us 

 too far to give here an account of the details of distribution. 



A compound ganglion behaves in some respects like a series of simple 

 ganglia. We have seen thatt he ganglion stellatum sends grey rami to a 

 series of spinal nerves. The nerve cells giving off these grey rami are 

 connected with the spinal nerves in much the same way as if they formed a 

 series of separate ganglia. Thus, a spinal nerve may be connected with 

 some of the grey rami, and not with the rest, but the former will in all cases 



1 Langley and Latham, Joum. Physiol., Cambridge and London, 1893, vol. xv. p. 242 ; 

 Harman {Joum. Anat. ami Physiol., London, 1898, vol. xxxii.) finds that in man the rami 

 of the second lumbar nerve have about two hundred medullated fibres, and that the rami 

 of the third lumbar have about twenty only. 



