354 PHYSIOLOGY CHAP. 



above or below its union with the vagus, or when the latter has 

 been divided above the point of junction. 



It thus appears that while the vaso-dilators almost always run 

 with the vaso-constrictors, their presence in the several nerve- trunks 

 can be detected, either by the physiologically distinct character of 

 their activity, or by their different course, their central origin, 

 and their morphologically distinct peripheral distribution. 



The data at present before us in regard to the course and 

 central origin of the vaso-dilators to the different regions are less 

 complete than those relating to the vaso-constrictors. 



The dilators contained in the cervical sympathetic were traced 

 by Dastre and Morat into the two branches of the Annulus of 

 Vieussens, the rami communicantes to the second to fifth spinal 

 nerves, and the anterior roots of the same. The majority unite on 

 their way to the periphery with the trigeminal, by an anastomosis 

 between the superior cervical and Gasserian ganglions. For after 

 section of the first branch of the trigeminal in the pterygoid- 

 maxillary groove, the vascular dilatation resulting from stimulation 

 of the cervical sympathetic appears only to a minimal degree in 

 the regions above indicated. On the other hand, with excitation 

 of the trigeminal, after division and degeneration of the cervical 

 sympathetic, dilatation of the facial vessels is obtained. This 

 shows that the dilator fibres of this nerve cannot all emerge by 

 the sympathetic and be of spinal origin ; others accompany the 

 trigeminus from its roots and are cerebral in origin. According 

 to Carlson (1907) the cervical sympathetic carries both vaso- 

 dilators and vaso-constrictors to the cat's submaxillary gland. 

 This fact had been overlooked by preceding investigators (Heiden- 

 hain, Langley, Bayliss), who speak only of vaso-constrictor fibres to 

 the salivary gland in the cervical sympathetic. This is due to 

 their observations having been made upon the dog (and other 

 mammals), in which the constrictors probably preponderate in the 

 cervical sympathetic, so that on stimulating the nerve the 

 constrictor effect alone is apparent. 



According to Langley, the dilators of the fore-limb originate in 

 the thoracic nerves (5th-8th pairs). The greater proportion of the 

 dilators to the hind-limbs run in the sciatic, a very few in the 

 crural. The work of Ostrournoff and others shows that these do 

 not arise in the sacral, but in the lumbar roots (2nd-4th pairs), 

 passing thence by the rami communicantes to the abdominal 

 sympathetic (and in a minority to the thoracic sympathetic) before 

 they unite with the sciatic. According to the observations of 

 Strieker, subsequently confirmed by Cossy, Vulpian, and others, 

 they do not arise like all other motor nerves in the anterior roots 

 alone, but also in the posterior roots of the fourth to fifth lumbar 

 pairs. This is the only well-proved exception to Bell's law (see 

 vol. iii.). 



