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Show 1895.] LUNGS OP SNAKES, AMPHISB.ENTDJE, ETC. 699 of larger branched vessels, and running as they do in a dorso-ventral direction they, so to speak, constitute a double or treble palisade between the two lungs [or to the left or right of the one lung which may be present]. Thus, firstly, the aorta gives off dorsal wards a whole series of vertebro-intercostal arteries to the vertebral column and adjoining body-wall, and ventralwards arteries to the oesophagus and stomach, while from these a series of veins passes to the portal system of the liver. With the exception of a few Amphisbsenidae, in which all or part of the last-mentioned veins run in the right dorsal hepatic ligament \ all the above-mentioned blood-vessels run in the median septum; and it will be seen that they form a well-marked palisade of vessels' across the space between the mid-dorsal line of the liver and the vertebral column. Secondly, starting from the aorta, we have arteries passing direct to the liver. Thirdly, in a number of elongated snake-like Lizards [as was, I believe, first described for Lizards by Hochstetter2 in Anguis and Pseudopus (Ophisaurus)] w e find that the main part of the vertebro-intercostal blood of the hepatic region of the trunk is returned by a series of veins that run from the dorsal body-wall to the liver via its right dorsal ligament3. N o w we find all of these above-mentioned series of blood-vessels fully developed in Snakes throughout the entire liver-region, as was admirably described by Schlemm4 as early as 1826; and they show us that the larger, or only functional, lung of Snakes is the right lung. 1 E. g. in Amphisbcena and Lepidosternon most or all of the veins from the oesophagus and anterior part of stomach run in the right ligament, which of course in these cases joins the alimentary canal. In Blanus cinereus part of the veins run in the right and part in the median ligament; while in the " Emphyodont" Pachycalamus and Trogonophis the veins run, as is, so far as I am aware, the rule for all other vertebrates, in the median membrane. 2 F. Hochstetter, " Beitrage zur Entwicklungsgeschichte des Venensys-tems der Amnioten. II. Reptilien," Morph. Jahrb. Bd. xix. Heft 3, pp. 428- 501, pis. xv.-xvii., Dec. 1892. 8 I find these veins running in the right dorsal ligament of the liver in Scelotes, Lygosoma, Lialis, and various Amphisbcenidce, e. g. Amphisbcena, Lepidosternon, Pachycalamus, and they doubtless occur in the other snake-like Lizards examined. There may be as many as five, as in Amphisbcena, and perhaps more, spaced throughout the whole length of the liver. A well-marked series of corresponding vessels is seen in Amphiuma and also in Ichthyophis, though in the last case they do not spring so directly from the vertebral column, but arise, as Hochstetter says has been described by Semon, from the unpaired vein between the mesonephric excretory organs which comes to take the place of the posterior cardinals of that region. 4 Fried. Schlemm, " Anatomische Beschreibung des Blutgefassystems der Schlangen," Zeitschrift fiir Physiologie (Ed. G. R. & L. Ch. Treviranus), Bd. ii. pp. 101-124, pi. vii. (Darmstadt, 1826). See especially pp. 115, 121 & 122. On p. 121 be notices the series of vertebro-intercostal veins flowing into the portal vein in the liver, which were so commonly omitted in the descriptions published between 1826 and Hochstetter's paper of 1892, while curiously the comparatively insignificant, but, if I may so say, orthodox, vein that brings back blood from the first few postcardiac segments was always duly noticed. |
