1904.] 



CIRCULATORY SYSTEM IX THE OPillDIA. 



335 



2nd branch is posterior, and passes back along tbe intestine to 

 join the first of the rectal vessels. It is pei'haps note^vorthy 

 that the point of origin fi'om the aoi'ta of the two mesentei'ic 

 vessels differs ; the supei-ior trunk arises latei';illy from the aorta, 

 whereas the inferior niesenteiic arises fi-oin that trunk in the 

 mid-ventral line. This conceivabl}' suggests a pi'evious state of 

 affaii's (phylogenetically speaking) when the intestine coiled 

 ventrally in its middle and posterior regions. 



Text-fi>;. {\7... 



SrV. 



Sri/ vSrl^ 



Part of arterial sxstem of Zcneiiis mticasiis. 



F.S., fat-body arteries ; Iiif.iiier., inferior mesenteric ; Inf.; intercostal arteries ; 

 Bee, rectal arteries ; Ben., renal ; Sr. V., suprarenal portal veins ; T., testis ; 

 Vet., vena cava. 



'^Lhe first of the rectal vessels, however, oi-iginates latei-ally like 

 the superior mesenteric. It springs from the aorta in a position 

 almost exactly between the two testes and about | inch in 

 front of. the inferior mesenteric. It has also, as will be men- 

 tioned, an intimate relation to one of the arteries of the fat- 

 body (see p. 337). The trunk i-uns backwards, crossing the 

 inferior mesenteric dorsally, and reaches the intestine at a point 

 aiaout opposite to the end of the first thii-cl of the posteiior testis. 

 Its behavioui- when it reaches the gut is precisely that of the 

 mesenteric arteries ; it divides into two branches, an anterioi- and 

 a posterior, so that it aids in the foi-mation of a continuous sub- 

 intestinal vessel running fi'om end to end of the gut. 



The second Rectal Artery arises behind the postei'ior testis. 

 and also springs latei-ally from the aortic trunk. Moreover, it 

 has exactly the same relations to a fat -body artery arising at this 

 spot as has the anterior rectal. 



The third Rectal Artery arises laterally (and on the same side 

 as the two anterioi- arteries) from the aoi-ta just behind the origin 

 of the second of. the renal arteries supplying the left kidney. 

 Behind this there are, at any rate, four moi'e arteries arising at 

 much shorter intervals. There may be more, but the injection 

 was deficient in this region of the bod}^ and rendered observation 

 difiicult. It is notewoi'thy that the rectal ai'teries become more 

 crowded towards the end of the body ; the 1st and 2nd are 

 further apart than the 2nd is from the 3rd. 



