INTESTrjiTAL CAKAL OF THE ICHTHTOPSIDA. 389 



the Baioidei. On reference to fig. 7, ii., whicli represents the 

 origins of these in the Thornback {Raia clavatd), it will be seen 

 that the coeliac (a.c.) and superior mesenteric, as ordinarily 

 described, arise far forwards and close together, as in the 

 majority of the higher Vertebrata, and that the so-called inferior 

 mesenteric (the right of the two lettered a.sm.) arises far behind 

 them, in a manner certainly suggestive of the mammal itself, and 

 such as might appear, were it true of all Plagiostomes, to justify 

 this comparison. In those Selachii of whose arteries we possess 

 a sufl&cient knowledge, the coeliac and superior mesenteric 

 arteries of the Batoids are represented by three trunks (fig. 7, 

 iii. to V. — the coeliac ; suj)enor, anterior, or anterior spermatico- 

 mesenteric ; and the lieno-gastric, of authors). In Acanthias the 

 two last named arise far back (v.), in close proximity to that 

 which Hyrtl likened to the inferior mesenteric trunk. 



Acanthias (fig. 7, v.) and Baia (ii.) represent the extreme 

 terms in the Plagiostome series, so far as our knowledge of the 

 arteries of their alimentary canal goes. The origins of the latter 

 are indicated to scale in the accompanying figures, and it will be 

 seen that there is a constancy of relationship between the coeliac 

 and so-called inferior (posterior) mesenteric vessels — the latter 

 shifts its position only in the Batoid, in which it is dragged 

 forwards, as it were in sympathy with the superior mesenteric, 

 which lies in close proximity to the coeliac *. 



No competent anatomist would hesitate to relegate the coeliac 

 and superior mesenteric arteries of Itaia (fig. 7, ii.), as ordinarily 

 described, to a common category ; nor would he, on first exami- 

 nation of Acanthias (fig. 7, v.), hesitate to similarly associate the 

 two arteries of the superior mesenteric series f with that termed 

 by Hyrtl and subsequent writers the "inferior mesenteric." 

 Herein lies the whole difficulty — are we justified in longer 

 referring, with Hyrtl, the vessel in question {a.sm. of fig. 1), to 

 the inferior mesenteric series ? 



In Scy Ilium (fig. 7, iv.) we meet with a condition essentially 

 transitional between the two extremes above mentioned {Eaia ii. 

 and Acanthias v.), inasmuch as the superior mesenteric arteries 



* I suspect that the changes incident upon the lateral extension of the body, 

 with its attendant abbreviation from behind forwards, may be here active. 



t I refer to these vessels as such for brevity, and in no want of respect for 

 either the work or nomenclature of my contemporaries. 



