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Show 154 MR. F. E. BEDDARD ON A PA R ASTERN I f M [June 7, with the dwindling bronchial rings, but with the vascular folds already spoken of. Microscopical examination shows them to he thick bands of muscular fibres, which aie not striated. The direction of these bands is circular, but they occasionally send off anastomosing branches as is shown in the accompanying sketch (text-fig. 28, p. 153). Occasionally, too, a small band detaches itself from one of the main hoops and ends upon the wall of the lung. Between the various bands the wall of the lung does not appear to be muscular. Towards the posterior end of the lung this arrangement is lost; there are no longer separate hoops of muscle but the walls are covered with a single sheet of musculature. It is clear from the above description, which may be compared with that of Platyurus on p. 150, that the structure of the lung differs very considerably in the two species. In Platyurus the lung lias retained to a much greater extent its pulmonary function, the lung-substance extending much further back than in Hydrus. The lung has, however, a less calibre, even proportionately, than in Hydrus, and there is no trace of so marked a conversion into a, " swim-bladder " with special muscles effecting its contraction and expansion as occurs in Hydrus. In the latter genus, moreover, the whole lung extends further back in the body than it does in Platyurus. 6. On the Presence of n Parasternum in tlie Lacertilian Genus Tiliqua, and on the Poststernal Ribs in that Genus. B y F r a n k E . B e d d a r d , M .A .. F .R .S ., Prosector to the Society. [Received June 3, 1904.] (Text-figures 29 & 30.) The use of the term " abdominal ribs" for the ventral and superficially placed cartilages, fibrous bands, or ossifications so distinctive of certain groups of Reptiles, is open to the objection that the term " ribs" has already a definite meaning attached to it. It implies cartilaginous, fibrous, or ossified rods which have or have had a connection with the vertebral column, whereas the so-called abdominal ribs have no relation whatever to the vertebral column, but are purely ventral structures formed between the plates of the ventral abdominal musculature. Furthermore, the term " abdominal ribs " is actually in use as descriptive of structures which are real ribs, and which have nothing to do with what other authors have called abdominal ribs. For example, 1V1 r. Boulenger, in his ‘ Catalogue of Lizards,' has referred, under the name of abdominal ribs, to the ventral legion of ribs in the Geckos, Cliamseleons, and some other forms, lying behind the sternum, which meet, pair by pair, in the ventral median line, thus completing a series of hoops encircling the abdomen. Inasmuch, as Dr. Gadow * justly points out, that * Cambridge Natural History : Amphibia and Reptiles, p. 504. |