72 THE PHYSIOLOCiY OF THE COMMON CRAYFISH. 



traverses the nervous cord (figs. 12 and 15), and divides 

 into an anterior (fig. 12, sa) and a posterior {iaa) brancli, 

 both of which run beneath and parallel with that cord. 



Fig lG.~Astacmf((viatUl'<.--The hearb ( x 4). A, from above ; B. from 

 below ; C, from the left side, aa, antennary artery ; rtc, alee cordis, 

 or fibrous bands connecting the heart with the walls of the peri- 

 cardial sinus ; h, bulbous dilatation at the origin of the sternal 

 artery ; ka. hepatic artery ; la, lateral valvular apertures ; oa, oph- 

 thalmic artery ; s.a, superior valvulnr apertures ; a.n.a, superior 

 abdominal artery ; st.a, sternal artery, in B cut off close to its 

 origin. 



A third arter}^ runs, from the front part of the heart, 

 forwards in the middle line, over the stomach, to the 

 eyes and fore part of the head (figs. 5, 12, and 16, oa) ; 

 and two others diverge one on each side of this, and sweep 



