386 PEOr. Q. B. HOWES ON THE 



with sucTi variations as I hare from time to time observed (a.im. 

 i. ii.). In one specimen (an adult $ ) ttere arose from the 

 aorta, a short distance in advance of the artery (iii.) normally 

 present, a single trunk (i.) ; this gave off, soon after its origin, a 

 small branch to tbe oviduct of the left side, but its main trunk 

 ran on to be distributed to the immediately adjacent wall of tbe 

 large intestine. In two other examples (both males) I have 

 noted tbe presence of two arteries (ii.) which, like the foregoing, 

 passed at once to the adjacent intestinal wall ; they differed 

 from the last-named only in their relative slenderness, and in 

 their exclusive restriction to the large intestine. The identity of 

 these vessels with those of the Salamander is most striking, 

 and when the parts under consideration in these animals 

 and tbe fish are (as delineated in PL I. figs. 1, 3, and 5) 

 reduced to the same size, the point of origin of the anterior of 

 the series is seen to coincide throughout. Wiedersheim speaks 

 of these vessels (33. p. 715) in the Salamander as arteries of the 

 rectum (' Mastdarm ') : in that they supply the greater portion 

 of tbe large intestine, this term is insufficient — for, on the 

 assumption (which can hardly be open to doubt) that the large 

 intestines of the Amphibia and Amniota are homologous, they 

 supply that section of the same which, in the ascending series of 

 Vertebrafca, becomes differentiated into the rectum and greater 

 portion of the colon. Here the mind again reverts to the 

 Mammal, and demands tbe declaration of homology between 

 these vessels and the inferior mesenteric artery of it and of the 

 higher Amniota, as the logical sequence to the facts. 



The area of distribution of the single inferior mesenteric artery 

 of the higber types being shown to coincide with that of the 

 series in the Amphibia (and Thornback), the question immediatelv 

 arises whether the condition of the first-named may not have 

 arisen, either from a collecting together of the several trunks, or 

 from atrophy of certain of the same, wholly or in part. The 

 leading brandies of these vessels usually lie, in the Salamander 

 (fig. 5), along the dorsal middle line of the intestine ; they there 

 anastomose freely to form a generally well-defined longitudinal 

 vessel, from which the side branches arise. In view of this, the 

 obliteration of, say, the three anterior trunks of the series, between 

 the aorta and the intestinal wall, would give us a condition 

 identical with that of the higher types (cf. ante, p. 384) ; and it 

 is conceivable that tbat realized in the latter may bave arisen in 



