INTESTINAL CANAL OF THE ICHTHYOPSIDA. 385 



of bifurcation, a well-marked vessel {a.im. fig. 4«, im. iii. fig. 2), 

 wliicli passes directly downwards, or but little obliquely back- 

 wards, for distribution to the immediately adjacent wall of the 

 large intestine. That viscus {i.l^ is in this animal, as in the 

 Ichthyopsida generally, very short ; and the vessel in question 

 supplies its posterior half — supplies, that is to say, that portion 

 of it which in the Mammalia becomes differentiated into at least 

 the rectum ; it has been termed by Wiedersheim, who first 

 described it (8. Abth. ii. p. 77), the " Arterie mesenterica inf. 

 oder A. hcemorrJioidalis superior,'' and by Marshall (23. p. 29) 

 the " liceriiorrlioidal artery T Inasmuch as it agrees, in every 

 detail, with the inferior mesenteric artery of the Mammalia and 

 higher Sauropsida (and especially with that of man to which the 

 term " inferior mesenteric " was first applied), it must be 

 similarly named "*. An unfortunate confusion has arisen be- 

 tween its main trunk and the superior hsemorrhoidal artery of 

 the higher Amniota, which is but a branch of its homologue; and 

 the burden of proof that it represents this branch alone lies with 

 those who have, as I believe, wrongly identified it. 



Turning from the Erog to the Salamander, we find usually 

 four such vessels represented {a.im., fig. 5). These were first 

 described by Hyrtl f, and subsequently by Eusconi (30. pi. vi. 

 fig. 1), who confused them with the efferent veins of the cloaca; 

 he, however, figured them with perfect accuracy, and they have 

 been more recently diagrammatically represented by Wieder- 

 sheim (33. p. 715, fig. 550 b). Hyrtl has described in Froteus, 

 Siren (I. c), and CryptolrancJius (19. p. 109) a series of vessels 

 having similar relationships. On examination, these arteries 

 are seen (fig. 5, a.im.) to agree, in origin and distribution, with 

 the inferior mesenteric artery of the Frog and of the Amniota 

 on the one hand, and with at least the anterior two of the four 

 vessels herein described for the Elasmobrauchs on the other. 



In all these animals individual variations aiFect, among other 

 parts, the arteries under consideration ; and, in the case of the 

 Erog, the former have hitherto escaped notice. Fig. 3 combines 

 the invariable condition met with in that animal {a.im. iii.) 



* Wiedersheim figures it {op. cit. p. 77, fig. 37), in error, as distributed to 

 the urinary bladder. I have never observed this arrangement. The allantoic 

 bladder of the Aruphibia receives its arterial supply, as does its homologue 

 among the Amuiota, from the iliac vessels. 



t Cf. " Lepidosircnparadoxa" Prag, 1845, p. 39. 



