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Show 698 MR. GERARD W. BUTLER ON THE [Nov. 19, As remarked above, and as is well known, tbe lungs of vertebrates are separated by one or more longitudinal septa. One of these contains the alimentary canal and is the median septum, marking the median plane of the body. Tbis is composed of the dorsal ligament of the alimentary canal, the gastrohepatic and hepato-cesophageal membrane, and the ventral, or so-called " suspensory," ligament of the liver. The other membrane is that one which is so conspicuous in tailed Amphibians and most Lizards, passing from the dorsal surface of the right liver-lobe to the dorsal body-wall. This membrane which, with its fellow on the left side [which, however, except in Amphisbaenidae remains almost or quite rudimentary, owing apparently to the mechanical obstacle to its development offered by the laterally displaced stomach], can be traced either in the adults or the embryos of other pulmonate vertebrates, has under one name or another received much attention from those who in the last seven years have written on the membranes and septa of the vertebrate body-cavity l. W e may, following Hochstetter, call it the " Hohlvenengekrose " (postcaval ligament), to express the idea that its hinder portion serves as a bridge for the posthepatic portion of the postcaval vein ; or we may call it the " right pulmohepatic ligament," to express the idea that it, like its fellow of the other side when present, arises in the embryo [I speak of Amniota,-Lacerta and Gallus~] in connection with the development of the lung and serves to attach it to the liver ; or we may call it simply the right dorsal ligament of the liver. As a matter of fact this membrane, with the exception of its posterior portion, does not occur in Snakes as a membrane distinct from the median or gastrohepatic, for the body-cavity does not extend between the right lung and the oesophagus and stomach as in Amphibia and most Lizards. It is, however, well seen in many snake-like Lizards. I have referred to these membranous septa because, as is so often the case with such membranes, they are tbe carriers of certain definite blood-vessels, which are to serve us as landmarks. The morphological position of these blood-vessels in relation to the various organs, and particularly to the lungs, w e first of all fix by the fact of their running in these membranes, whose relations are so well known and clear in Lizards, aud we then can use these same blood-vessels as landmarks in Snakes, where the membranous septa would otherwise be hardly traceable. Fortunately for our purpose, in Snakes, as in some elongated snake-like Lizards and Amphibians, the blood-vessels referred to tend to occur as series of simple vessels instead of as a lesser number 1 F. Hochstetter, " Ueber das Gekrose der hinteren Hohlvene," Anat. Anz. Bd. iii. pp. 965-974 (1888). Ravn, Archiv fur Anat. u. Phys., Anat. Abth. 1889, pp. 123-154 & 412. G. W . Butler, Proc. Zool. Soc. 1889, pp. 452-474. H. Klaatsch, " Zur Morphologie der Mesenterialbildungen am D a rmkanal der Wirbelthiere. Theil I. Amphibien u. Reptilien," Morph. Jahrb. 1892, pp. 385- 450. |