1906.] SYSTEM OF CERTATX SPECIES OF AXURA. 1021 



with the large intestine, giving off twigs on the way, to the cloacal 

 region ; but in this respect R. hexadactyla was an exception, the 

 main vessel running freely in the mesentery beside the gut, while 

 its subdivision formed a series of anastomoses which gave it a 

 fenestrated structure (text-fig. 147, p. 1019). Near the distal end 

 of this posterior vessel an anastomosis is often formed with the 

 A . mesenterica inferior from the aorta, but the occurrence or non- 

 occurrence of this seems to be quite accidental. 



In connection with the A. mesenterica anterior a point may be 

 mentioned here which possibly has not escaped the notice of others, 

 namely, the giving off of a vessel from a branch of the arteiy to a 

 region of the intestine quite outside the sphere with which that 

 branch and its vessels are concerned. Notwithstanding the 

 approximation of diflferent regions of the intestine that may occur 

 owing to the folding of the mesentery, there is normally no true 

 overlapping of the vessels ; that is to say, their respective regions of 

 distribution remain distinct, and even the minor vessels do not cross 

 one another. But in certain cases a departure from this occurred. 

 Thus in^. clamata (text-fig. 145, p. 1015) one of the vessels of the 

 median ramus crossed undei* all its fellows behind it and went out 

 of its way, so to speak, to the extreme end of the small intestine ; 

 and in a moi-e I'emarkable degree, one of the vessels of the proximal 

 ramus struck across under the whole of the median ramus to a 

 point on the intestine behind all the vessels of the latter. Both 

 of these points were rejjeated in the second specimen of R. clamata. 

 In R. catesbiana there was no crossing of the vessels of the median 

 ramiits, but a vessel from the 2)'>^oximal ramus passed back under 

 all those of the 'inedian ramus, reaching the intestine behind 

 them ; and the-same was the case in B. tnauritanicus. In R. tem- 

 poraria one individual had the same irregular vessel from the 

 proximal ramus only ; another individual had two such vessels 

 from the median rwmus only. In the other species nothing of 

 the kind occurred. There was sometimes a very close attachment 

 between these irregular vessels and those crossed by them, but 

 there was no union between them. In fact, while the extreme 

 distal portions of the arteries often combine, even so as to form a 

 continuous vessel along the wall of the gut, I observed no case of 

 anastomosis where the vessels lie free in the mesentery, excepting 

 the fenestrated arrangement previously mentioned in R. hexa- 

 dactyla near the wall of the large intestine, and a union between 

 two vessels of the A. gastrica sinistra close to the stomach in one 

 specimen of R. cla'niata. 



Aa. urogenitales. — These ai-teries have often been inaccurately 

 described as arising from a series of unpaired stems which bifurcate 

 right and left. As pointed out by Gaupp, such an arrangement 

 is subject to much variation. In two of the species under con- 

 sideration, namely R. hexadactyla and B. horeas (text-fig. 149, 

 p. 1023; text-fig. 151, p. 1026), they all of them arose from unpaired 

 stems in the aorta, which divided into right and left branches 

 to the urogenital organs on either side. But in all other cases, traces 



