446 



SYMPATHETIC NERVE. 



branches between the sympathetic and cere- 

 bral nerves, they also regard it as probable 

 that the greater number of the fibres in the 

 communicating branches run peripherically. 

 In the fish and bird they also found that the 

 fibres of the communicating branches were di- 

 rected partly towards the centre and partly to- 

 wards the periphery. In small animals belong- 

 ing to the class mammalia, such as the rat and 

 mole, as well as in small dogs and cats, they 

 found, on examining the communicating 

 branches with the microscope as before, that 

 the fibres passed both inwards towards the 

 centre, and also outwards towards the peri- 

 phery, and that the latter in many cases ex- 

 ceeded the former. 



As already mentioned, there are commonly 

 two branches of communication between 

 each of the spinal nerves and the sympa- 

 thetic in the higher animals. The one of 

 these presents a white appearance, resem- 

 bling more or less the ordinary nerves of 

 the cerebro-spinal system; the other has fre- 

 quently a more gray aspect, approaching in 

 this respect the appearance of the sympa- 

 thetic nerves. Sometimes the white cord 

 presents the appearance of being composed 

 of a white and a grayer portion running to- 

 gether. As regards the minute structure of 

 the rami communicantes, the whiter portion 

 consists entirely of tubular nerve-fibres, both 

 of the coarser and finer varieties . there are 

 also not unfrequently present fibres which 

 appears to be intermediate in point of breadth. 

 In general the broader variety of fibres ap- 

 pear to be more numerous than those which 

 belong to the finer variety. According to 

 Kolliker, the relation between them is much 

 the same in point of number as in the pos- 

 terior roots of the spinal nerves. The gray 

 portion, as is stated by Todd and Bowman, 

 contains a large proportion of fibres belonging 

 to the gelatinous variety : in young animals 

 it is often entirely composed of structures 

 agreeing in character with the gelatinous 

 fibre. In the full-grown animal also it often, 

 when examined without addition of reagents, 

 presents the appearance of being altogether 

 composed of these fibres. Addition of dilute 

 solution of soda, however, always brings into 

 view a number of tubular nerve-fibres, which 

 belong to the finer variety. The relation be- 

 tween the tubular fibres and those of the 

 gelatinous kind as regards number, is much 

 the same as in many of the branches of the 

 sympathetic, especially in the smaller twigs 

 distributed to the blood-vessels. Occasionally, 

 however, especially in the rabbit and cat, this 

 portion is found to be almost exclusively 

 composed of fine tubular nerve-fibres : the 

 gelatinous fibres being present only in small 

 numbers. In its appearance as seen by the 

 naked eye, as well as in its microscopic 

 structure, the grey portion of the rami com- 

 municantes agrees in character with the 

 branches of the sympathetic, and would ap- 

 pear to be an offset from the same to the 

 cerebro-spinal nerves. This is rendered 

 more probable by the observation of Dr. 



Beck, that the grey portions on leaving the 

 ganglia send off small branches to the neigh- 



Fig. 292. 



From a gray communicating filament between the sym~ 

 pathetic, and one of the lumbar nerves in the Cat, 

 treated with acetic acid, showing fine nerve-Jibres, 

 and nucleated fibres of Remak. {Mag. 250 diam.*) 



bouring vessels, and are reduced in size before 

 reaching the spinal nerves. Moreover, Kol- 

 liker has sometimes observed a small gan- 

 glion present upon them, which, on exami- 

 nation, was found to present the structure of 

 the sympathetic ganglia, and which gave 

 origin to the fibres with which it was con- 

 nected. 



As regards the white portion of the rami 

 communicantes, there can be no doubt that all 

 the broad tubular fibres contained in it are 

 fibres which are transmitted from the nerves 

 of the cerebro-spinal system. This is proved by 

 the fact that all the tubular fibres which are 

 supposed to originate in the ganglia do not be- 

 long to the broader, but to the finer variety. In 

 regard to the finer variety of tubular nerve- 

 fibres occurring in this portion, inasmuch as 

 similar fibres are present both in the anterior 

 and posterior roots of the spinal nerves, they 

 ma}' be regarded either as fibres sent from the 

 spinal cord to the sympathetic, or they may 

 be fibres which are transmitted from the latter 

 to the cerebro-spinal nerves. On tracing 

 the white portion of the rami communicantes 

 backwards to the spinal nerve, it is found to 

 apply itself to the latter generally in a direc- 

 tion more or less central. On attempting to 

 separate the two by means of needles, though 

 several of the fibres break across, yet the di- 

 rection of these, as well as of the others, ap- 

 pears to be towards the centre. When the 

 corresponding spinal nerve, along with its 

 communicating branch, is dissected out, and 



