72 . THE PHYSIOLOGY OF THE COMMON CRAYFISH. 
traverses the nervous cord (figs. 12 and 15), and divides 
into an anterior (fig. 12, sa) and a posterior (iaa) branch, 
both of which run beneath and parallel with that cord. 
Fig. 16.—Astacus fluviatilis.—The heart (x 4). A, from above ; B, from 
below ; C, from the lefiside. aa, antennary artery ; ac, ale cordis, 
or fibrous bands connecting the heart with the walls of the peri- 
cardial sinus; }, bulbous dilatation at the origin of the sternal 
artery ; ha, hepatic artery ; Ja, lateral valvular apertures ; oa, oph- 
thalmic artery ; s.a, superior valvular apertures ; s.a.a, superior 
abdominal artery; st.a, sternal artery, in B cut off close to its 
origin. 
A third artery 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 
