II.] THE CRAYFISH AND LOBSTER. 22 5 



tributing branches metamerically to the appen- 

 dages, muscles and parts adjacent. 



/?. The postero-ventral (inferior-abdominal) artery ; 

 a median trunk extending back to the telson. It 

 also distributes branches metamerically to the 

 adjacent parts. 



The above trunks furnish the main vessels to 

 the reproductive organs. They are, on either 

 side — a dorsal one, arising from the sternal artery 

 soon after it leaves the heart and distributed 

 to the genital gland and duct; a ventral one, 

 arising from the base of /?, and distributed to the 

 terminal segment of the duct alone. 



The sternal trunk may pass to either side of the 

 alimentary canal. If the injection be successful, 

 it will be found that the vessels distributed to the 

 ends of the intestine and genital ducts debouching 

 on to the exterior, terminate in special capillary 

 networks. 



e. The antennary artery ; arising from the antero- 

 dorsal region of the heart, immediately external to 

 b. Its main trunk runs downwards and forwards, 

 passing round (external to) the adductor rhandibuli 

 muscle and immediately under the carapace, to 

 terminate anteriorly in the antenna. It gives off 

 on its course — 



a. The gastric artery ; arising close behind the pos- 

 terior gastric muscle, and distributed to the 

 stomach (fore-gut). 



j3. Branches to the gastric muscles, several en route. 



y. A rostro-antennary branch ; arising from the main 

 M. 15 



