APPENDIX III 



297 



but composed of a number of fibres attached to the walls 

 of the heart over a considerable area around the ostia. 

 They may either be contractile and serve to expand the 

 heart, or, more probably, elastic and restore the heart to its 

 expanded condition after each contraction. 



The blood, after circulating through the head, runs 

 ventrally backwards through the intestinal sinus, towards 



Fig. 66.— Diagram to illustrate the plan of the circulation in the anterior part of the 

 body. The blood propelled by the heart {h) through the head, is returned 

 through the intestinal sinus {is) from which in each segment it escapes ventrally 

 into the limbs. Its course is indicated diagrammatically by the arrows (/). From 

 the limbs it returns through the dermo-muscular sinus in each segment into the 

 cardial sinus (^.s-). i, intestine; ac, aorta cephalica; p, points of attachment of 

 the dorso-ventral muscle bands. 



the posterior end of the body. Near each pair of limbs, 

 the membrane forming this sinus appears to be fenestrated, 

 the openings being regulated by special muscles (?). Through 

 these windows the blood streams down over the ventral 

 cord and into the limbs on each side ; it runs along the 

 ventral face of the limbs, returning along the dorsal. On 

 its way back it is guided into the gills, and thence back 



