INTESTINAL CANAL OF THE ICHTHTOPSIDA. 391 



Salamandrine series differ from the corresponding vessels of 

 other Vertebrata only in the fact that their main trunks show but 

 little signs of forward displacement. In that they leave the 

 dorsal aorta nearly at right angles to the long axis of the body, 

 they approximate towards the condition of the inferior mesen- 

 teric arteries (cf . ante, p. 388) ; there is, however, a very marked 

 gap * between the two sets of vessels, and, of the two, the 

 anterior are by far the most closely aggregated {cf. fig. 4). 

 Fusion of these, more or less marked, would give us the varying 

 conditions met with in the other Vertebrata. I have satisfied 

 myself that reduction in their number, such as that figured by 

 Wiedersheim (loc. cit.), results either from fusion of a couple 

 of the anterior mesenteric trunks (a.sm.), or from confluence 

 between the most anterior of these and tbe coeliaco-mesenteric 

 artery (a.cm.). In this we have evidence of a process of change 

 identical with that to which the facts concerning the inferior 

 mesenteric vessels appear to point (cf. ante, p. 387) ; taken in 

 conjunction with that above described in Acanthias (p. 390), it 

 points unmistakably to the conclusion that the less numerous 

 coeliac and superior mesenteric arteries of the other Yertebrata 

 may have arisen (as I have attempted to show for the inferior 

 mesenteric) from a more numerous series, by concrescence. If 

 I am right in referring tbe posterior mesenteric artery of the 

 Plagiostome fishes to this coeliaco-anterior-mesenteric series (and 

 this, in the long run, is the leading conclusion for which I am 

 contending, so far as the blood-vessels are concerned), Hyrtl's 

 observation (18. p. 13), that in Torpedo it is represented by two 

 arteries which proceed side by side to the processus digitiformis 

 and adjacent parts, is very welcome ; for it suggests that in that 

 which I would term the supernumerary vessel we may, in all 

 probability, be dealing with the representative of one which 

 has been lost in the allied forms. The arteries of this series 

 vary in number, in the Salamander, from seven to six ; in the 

 knowledge of the fact discovered by Hyrtl they do so, in the 

 Plagiostomes, from five to three ; and when it is seen that they 

 are to-day showing signs of concrescence (cf . ante, p. 390), we are 

 enabled to point to the existence of a gradational series which 

 very strongly favours the conclusion that the vessels repre- 



* This appears to have been exceptionally marked in the individual figured 

 by Wiedersheim (33^ fig. 550 b). 



