PROF. HOWES ON INTESTINAL CANAL OE ICHTHTOPSIDA. 381 



On the Intestinal Canal of the Ichthyopsida, with especial 

 reference to its Arterial Supply and the Appendix Digi- 

 tiformis. By G. B. Howes, F.L.S., E.Z.S., Assistant 

 Professor of Zoology, Normal School of Science and Eoyal 

 School of Mines, S. Kensington. 



[Eead 20fch March, 1890.] 



(Plates I. & II.) 



CONTENTS. 



Page 

 I. On the Arteries of the Inferior Mesenteric Series, in the 



Ichthyopsida 381 



II. On the Arteries of the Coeliac and Superior Mesenteric Series, 



in the Ichthyopsida 387 



III. On certain Appendages of the Intestinal Wall of the Ichthyo- 



psida, in relation to their Arterial Supply 393 



IV. On the Caicum of the Teleostei .'. 400 



V. In Conclusion 406 



VI. List of leading Authorities referred to 407 



VII. Explanation of the Plates 408 



I. On the Arteries of the Inferior Mesenteric Series, in the 

 Ichthyopsida. 



The alimentary canal and its appended glands in the Plagiostome 

 fishes receive their arterial supply from three or more trunks 

 arising from the dorsal aorta (Plate I., ao., fig. 1). Of these, the 

 least variable are those which form the extreme anterior and 

 posterior members of the series as hitherto described {cf figs. 7, 

 iii., iv., v.), viz. the so-called coeliac and inferior mesenteric 

 arteries. In addition to these there are usually present two 

 arteries which, unlike the rest, are paired, being derivative of 

 the iliac vessels {a.i., fig. 2) ; these, the paired nature of which 

 has not before been detected*, pass directly backwards and 

 inwards to reach the posterior wall of the cloaca, in a manner 

 suggestive of the hypogastric arteries of the higher Vertebrata. 

 The vessels alluded to above as "hitherto described" are so well 

 known, and their courses and distribution have been so fully 

 dealt with by Monro, Hyrtl, Parker, and others, that detailed 

 reference to them here is unnecessary. The distribution of the 



* Hyrtl has recorded the presence of one {Rata clavata) on the left side 

 only (18. p. 30). 



LINN. JOUEN. — ZOOLOQ-Y, VOL. XXIII. 27 



