THE CIRCULATION THROUGH SPECIAL ORGANS 427 



drawn from the systemic circuit, generally give rise to mental -and 

 bodily fatigue. These symptoms are also observed whenever the 

 tonicity of the splanchnic blood-vessels is lost in consequence of general 

 nervous debiHty, irritation of the intestines, and other conditions. 



Concurrently, it may be gathered that the stimulation of the distal 

 end of the greater splanchnic nerve must occasion a transfer of blood 

 from the splanchnic area into the general circulation, because the 

 vasoconstriction resulting in consequence of this procedure, forces 

 a large quantity of blood out of these channels into the veins and the 

 general circuit and prevents at the same time a corresponding influx 

 of arterial blood. The systemic blood pressure, therefore, is rapidly 

 increased, but naturally, this augmentation cannot exceed physiolog- 

 ical limits, because while the arterial blood does not find free access to 

 the splanchnic organs, it is still in a position to leave the arterial chan- 

 nels by way of the carotid and femoral arteries.^ Thus, while the 

 stimulation of the splanchnic nerve lessens the flow through the organs 

 innervated by it,^ the circulatory conditions in the central venous 

 system remain practically unaltered. 



The Depressor Nerve. — The function of this nerve has been de- 

 scribed in detail in one of the preceding chapters (page 329). It is 

 a sensory nerve and conducts impulses from the heart to the cardiac 

 and vasomotor centers. Its function is to produce a general reflex 

 vasodilatation, and therefore a fall in the systemic blood pressure. In 

 the nature of things, this effect can only be obtained by the stimulation 

 of either the intact nerve or of its central or cephalic stump. It has 

 been stated above that marked depressor effects may also be obtained 

 with the help of the thoracic sympathetic nerve and its branches. 



CHAPTER XXXV 



THE CIRCULATION THROUGH SPECIAL ORGANS 



A. THE CORONARY CIRCULATION 



In man the orifice of the right coronary artery is situated in the 

 anterior sinus of Valsalva, whence this blood-vessel passes forward 

 and follows the right auriculoventricular groove until it reaches the 

 interventricular groove. At this point it divides into two branches, 

 the smaller of which continues onward in the left auriculoventricular 

 groove, and the larger in the inferior interventricular groove. The 

 left coronary artery arises from the left fossa of Valsalva and, passing 

 backward, divides at the left auricular appendix into two branches, 



1 Edwards, Am. Jour, of Physiol., xxxv, 1914, 15. 



2 Burton-Opitz, Quart. Jour, of Exp. Physiol., iv, 1912, 83. 



