ANGLE OF ORIGIN OF VESSELS 381 



of the branch vessel nor by the radius of the main vessel, but by 

 the ratio of these two quantities. For any particular value of the 

 ratio rjR, we have therefore a constant value of d ; that is, all 

 branches of equal radius will be equally inclined to the main 

 artery. 



(1) In particular, if the artery bifurcates into two equal branches, 

 the angles of bifurcation will be equal. 



(2) If r is so small compared with R that the amount of blood 



r 

 going to the branch is almost negligible, then cos 6 = -^ tends to 



be infinitely small, i.e. angle 6 will be close to 90°. 



(3) If r differs but slightly from R it is obvious that cos 6 tends 

 towards the limiting value = 1, i.e. 6 will be very small. 



While these statements are true as they stand they are not the 

 whole truth. Other factors come to bear on the angle of origin 

 and produce modifications not comprehended in Hess's Law. 



Further Eeading 



LovATT Evans. " Recent Advances in Physiology," J. & A. Churchill. 

 Bainbridge. "The Physiology of Muscular Exercise," Longmans, Green 

 &Co. 



