I^O PATTEN AND REDENBAUGH. [Vol. XVI. 



line, supplying the tissues on the haemal side of the body in 

 the neighborhood of the proventriculus, and divides at the 

 anterior margin of the carapace to form two anterior marginal 

 arteries. These follow the edges of the carapace around to the 

 posterior angles of the cephalothorax, where they are joined 

 by branches from the arteriae collaterales. 



The aortic arches (Pls.VIII and IX, Figs. 3-5 and 8, aojx) 

 curve downward upon each side of the proventriculus, supply 

 this organ and the oesophagus, and then follow the oesophagus 

 backward to the vascular ring, which encloses the nerve collar. 

 The vascular ring gives off arteries anteriorly to the oesopha- 

 gus, to the tissues in the median line neural to the oesophagus, 

 and to the median and lateral eyes. The chelicerae, five pairs 

 of ambulatory appendages, chilaria, and operculum also receive 

 large arteries from the vascular ring. The ventral artery (PI. 

 IX, Fig. 6, v.ar.), which sheathes the ventral cord, is given off 

 from the posterior side of the ring. The longitudinal abdominal 

 muscles, the neural side of the intestine, and the five pairs of 

 gills receive their blood supply from the ventral artery. Poste- 

 riorly this artery divides into a number of branches, some sup- 

 plying the muscles of the caudal spine, but the main branches 

 pass on either side of the rectum to the interior of the caudal 

 spine. A little in front of the anus these arteries give off 

 branches which, after supplying the rectum, pass haemally on 

 each side of the rectum and anastomose with the arteria abdomi- 

 nalis superior {s.a.ar.). 



The origins of the four pairs of lateral arteries {l.ar.^~^) and 

 their union with the arteriae collaterales {car.) have already 

 been described. An interesting variation, however, sometimes 

 occurs. A fifth lateral artery (PI. IX, Fig. .5, i.ar.^) has been 

 found arising from the base of the left aortic arch, anterior to 

 the aortic valve, and opposite the rudimentary ostia {r.os ). This 

 artery has no semilunar valves, but it joins the collateral artery 

 just as do the other lateral arteries. In the same specimen in 

 which this lateral artery was found, a small artery was found in 

 the corresponding position upon the opposite side, but this did 

 not connect with the collateral artery of that side. It supplied 

 the tergo-proplastral muscles. 



