x VASCULAR MUSCLE AND NERVES 343 



time to acquire the characteristics of venous blood, while the 

 pulse wave of the arteries passes beyond the capillaries, and 

 reaches the small veins (Fig. 155). 



There are, accordingly, constrictor and dilator nerves to the 

 blood-vessels : the former correspond to the systolic, the latter to 

 the diastolic, nerves of the heart. Vascular rhythm and tonicity 

 are analogous to cardiac rhythm and tonicity. Just as the 

 innervation of the heart regulates the circulation as a whole, so 

 the innervation of the vessels regulates the circulation in the 

 several vascular regions. The same questions as were examined 



FIG. 155. Operative procedure for exposing submaxillary gland, duct, nerves and vessels. 

 (Cl. Bernard.) Gsm, Submaxillary gland ; D?c, Wharton'.s duct, into which a glass cannula is 

 inserted to draw off the saliva secreted by the gland ; Db, Bertholin's duct to sublingual ; 

 Nl, lingual nerve ; Ct, chorda tympani, running to gland along with excretory duct ; C, carotid 

 accompanied by small nerve branches of sympathetic ss ; Vje, external .jugular vein ; V, 

 efferent vein from gland ; Ni, hypoglossal nerve ; Md, anterior half of digastric muscle, lifted 

 by hook ; Mmj, mylo-hyoid muscle, cut so as to expose the lingual nerve, and excretory ducts 

 beneath it ; Mn, maseter muscles. 



and discussed in studying the active movements of the heart 

 crop up in the study of the active movements of the vessels. 

 We must therefore consider separately the rhythm and the tone 

 of the vessels, the vaso-constrictors, and the vaso-dilators, in the 

 better-known vascular regions. 



II. The slow rhythm of dilatation and constriction, as first 

 described by Schiff for the vessels of the rabbit's ear, is no isolated 

 phenomenon. It was observed by Wharton Jones in the vessels ot 

 the bat's wing, by Saviotti on the frog's peritoneal arteries, by 

 Riegel in the small mesenteric arteries and web of the same 

 animal. In this category must also be included the long irregular 

 waves "of the third order," which are independent of cardiac rhythm 

 and respiratory movements, and were first noted in blood-pressure 



