INTESTINAL CAJfAL OF THE ICHTHTOPSIDA. 383 



describes (18. p. 13) a single very small artery arising imme- 

 diately in front of the ci'ural vessels and becoming distributed to 

 the cloaca — together with the hinder ends of the kidneys and 

 related vasa deferentia. 



PI. I., fig. 1, represents the parts concerned in one of my 

 specimens {JRaia clavata, adult $ ), as dissected from the side after 

 injection with French blue. The cloaca of these animals {cV) 

 becomes, as is well known, greatly modified — especially in the 

 female — in relation to the genital ducts {pd.); these approximate 

 posteriorly in relation to a chamber (oviducal recess, cV") formed 

 by partial subdivision of the cloaca. The arteries in question lay 

 (a.«m.) immediately in front of the approximated ends of the genital 

 ducts ; they arose between the kidneys, the anterior one leaving 

 the aorta at about the middle of these organs *. These vessels 

 lay, like the so-called posterior mesenteric (a.sm.), in the folds of 

 the suspensory ligament of the so-called rectum ; unlike that, 

 however, they passed (not obliquely backwards but) directly 

 downwards, at right angles to the long axis of the body. The 

 distance between them was far less than that between the 

 anterior one and the so-called posterior mesenteric. I have, in 

 two instances, detected the passage from the extreme base of the 

 aorta, immediately before the point of origin of the iliac vessels, 

 of a couple of very delicate trunks for the post-cloacal Avall 

 (a.im., fig. 1). Similar vessels may be present in Acanthias ; 

 they arise in the immediate vicinity of the bases of the kidneys, 

 and reach the cloaca posteriorly to the genital ducts. I take 

 them to be the homologues of that vessel referred to by Hyrtl 

 in Torpedo. Neither set of arteries supplied (with the exception 

 named above), so far as I was able to ascertain, anything but 

 that portion of the intestinal canal immediately adjacent to its 

 point of origin. 



It is clear from the foregoing that any comparison which shall 

 now or in future be instituted between the arteries of the 

 posterior portion of the Skate's intestine and those of the corre- 

 sponding parts in other Vertebrates must take into consideration 



* In one specimen observed, the anterior renal artery of the exposed side 

 arose at this point together with the intestinal vessel named, from a common 

 trunk. I am indebted to my demonstrator, Mr. M. F. Woodward, for the 

 knowledge of a specimen {Raia maculata, 9 ) i^^ wiiich the posterior renal 

 artery of either side gave off a vessel to the cloacal wall, a short distance 

 behind the oviduct. 



27* 



