1802.] Cervical and Upper Thoracic Sympathetic Fibres, <Jr. 447 



vertebral canal, and the effects of the stimulation observed. The 

 results were as follows : 



None of the lower cervical nerves produces any of the effects 

 which can be produced by stimulating the upper thoracic or cervical 

 sympathetic ; i.e., the lower cervical nerves send no efferent visceral 

 fibres to the sympathetic. 



The pupil receives dilator fibres from the 1st, 2nd, and 3rd thoracic 

 nerves. The relative effect of these nerves upon the pupil varies 

 somewhat in different animals of the same species, and varies con- 

 siderably in animals of different orders. In the cat and dog, both 

 the 1st and 2nd thoracic nerves cause great dilation of the pupil ; in 

 the cat, as a rule, the 1st produces greater dilation than the 2nd 

 thoracic, but this is not always the case, and sometimes the 2nd is 

 more powerful than the 1st thoracic nerve; the 3rd thoracic nerve 

 has a comparatively slight action, and the extent of its action varies : 

 in some cases the dilation produced by it is readily observed, in others 

 it requires special attention. In the rabbit, the 2nd thoracic nerve is 

 the chief dilator nerve for the pupil ; the 3rd thoracic nerve produces 

 a considerable dilation, but less promptly than the 2nd; the 1st 

 thoracic has the least action of the three, and in some cases has a 

 very slight effect. 



The nerve-fibres causing retraction of the nictitating membrane and 

 opening of the eyelids have in the dog and rabbit the same origin as 

 the dilator fibres for the pupil. In the cat, their origin is somewhat 

 more extended ; a few fibres arise from the 4th thoracic nerve, and 

 occasionally a very few from the 5th thoracic nerve. 



The vaso-motor fibres for the head* arise in the cat from the first fivo 

 thoracic nerves, in the dog from the first four, and probably to a 

 slight extent also from the 5th. The 1st thoracic nerve has a slight to 

 moderate vaso-motor effect in the dog, a less and inconstant effect in 

 the cat ; the 2nd and 3rd thoracic nerves cause complete and rapid 

 constriction of the small arteries on the same side of the head ; the 

 4th thoracic also causes complete contraction, but more slowly than 

 either the 3rd or the 2nd : in the dog its effect is less than in the cat ; 

 the 5th thoracic nerve has in the cat a distinct though less effect than 

 the 4th ; in the dog its action is doubtful. 



In the rabbit, the vaso-motor nerves for the ear arise from the 2nd 

 to the 8th thoracic nerves inclusive ; the 5th nerve has usually the 

 most rapid effect ; passing upwards or downwards, the effect decreases ; 

 the 2nd and 8th nerves usually cause complete constriction in a part 

 only of the auricular artery. 



The secretory fibres for the sub-maxillary gland of the cat and dog 

 have the same origin as the vaso-motor fibres for the head. The 2nd 

 thoracic causes secretion more readily than any other nerve. 

 * Certain parts only of the head have been observed. 



