72 THE PHYSIOLOGY OF THE COMMON CRAYFISH. 



traverses the nervous pord (figs. 12 and 15), and divideiB 

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

 both of which run beneath and parallel with that cord. 



Fig 16. — Astaovs fltiviatilis. — The heart ( x 4). A, from above ; B, from 

 below ; C, from the left side, aa, antennary artery ; ac, ate cordis, 

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

 cardial sinus ; i, bijlbous dilatation at the origin of the sternal 

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

 thalmic artery • s.a, superior valvular apertures ; hmm-, superior 

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

 origin. 



A third artery runs, from the front part of the heart, 

 forwards in the middle Hne, 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 



