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Show 5 2 0 MR. F. E. BEDDARD ON THE VASCULAR AND [May 1, able to add the description of the lung in the Hamadryad *, which shows a new form of tracheal lung or rather air-sac, and an account of the lung in the two sea-snakes Platyurus colubrinus and Hydrus platyurus f , extending the observations of Cantor upon one of these, and I have lately brought forward some evidence in favour of regarding the existence of the tracheal lung as typical for the SquamataJ. I have now to direct attention to further facts collected during the last few months which fill in several lacunae in our knowledge of the respiratory system in the Ophidia, and permit of some more general statements than could be made by previous observers, who had examined comparatively few species and genera. I am able considerably to extend the knowledge of the occurrence of the tracheal lung, and thus to put upon a firmer basis my view that this part of the lung is not a secondary development, but that its presence is a primary condition of the lung in those reptiles, and probably in the allied Lacertilia. In the following pages I direct attention to the structure of the lung's in a few Colubrine Snakes. I have already cD %f referred to the lungs of certain Boidae §. The lungs of Coluber corais are in several respects remarkable. In this serpent the tracheal lung is developed to a very great extent, but as an air-sac. The trachea ceases to be a closed tube almost immediately after its origin; half way between the free and the attached ends of the mandibles the trachea opens out into a gutter. It is not a question here of a narrow membranous interval dorsally between the free ends of the tracheal rings. These extremities are connected by a wide thin-walled sac several times the diameter of the trachea itself. Towards the heart this tracheal lung becomes slightly honeycombed in structure and vas-cularised; but it is a very small tract that can possibly serve as an organ of respiration. The lung proper begins at the heart; there is no change at this point either in the calibre of the tracheal lung, which is continuous with the thoracic lung, or in the form of the tracheal gutter. The latter ceases almost immediately after the commencement of the thoracic lung. An aperture leads into the rudimentary left lung. This lung although small is evidently functional; its walls have the usual honeycomb structure and are red with blood capillaries. Moreover, the cartilaginous semirings of the trachea are continued for a short distance into the second and smaller lung. The large and principal lung retains its vascularity down to just after the beginning of the liver. After this point it is merely a thin-walled air-sac like the tracheal lung. Its length is unusual, at least if it be compared, for instance, with the lungs of the Python. It is traceable nearly to the cloaca posteriorly. It must therefore form a very efficient swim-bladder or enable the snake to puff itself * " On the Trachea, Lungs, &c. of the Hamadryad," P. Z.S. 1903, vol. ii. p. 319. f " On the Visceral Anatomy of Pelagic Serpents," ibid. 1904, vol. ii. p. 14-7. x " Contributions to the Anatomy of the Ophidia," ibid. 1906, vol. i. p. 41. § Supra, p. 515. |