224 



MANUAL OF ZOOLOGY 



SECT. 



end of the heart arise five vessels, and from the posterior 

 end two, which are practically united at their origin. 



All these arteries branch extensively in the various organs 

 they supply, becoming divided into smaller and smaller 



cftm, 





FIG. 118. Transverse section of thorax of Crayfish, diagrammatic, abm. ventral 

 abdominal muscles ; bf. leg ; bm. ventral nerve-cord ; d. intestine ; dbm. dorsal 

 muscles of abdomen ; ef. wall of thorax ; h. heart ; k. gills ; kd. gill-cover ; 

 /.liver; or. ovary ; pc. pericardia! sinus; sa., sn. sternal artery ; 7<s. ventral 

 sinus. The arrow shows the direction of the blood-current. (From Lang's 

 Comparative Anatomy.} 



offshoots, which finally end in microscopic vessels called 

 capillaries. These latter end by open mouths which com- 

 municate with the blood-sinuses (Fig. 119, s.), spacious 

 cavities lying among the muscles and viscera, and all com- 

 municating directly or indirectly, with the sternal sinus 



