520 MB. F. E. BEDDARD OK 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 Platyunis coluhrimis 

 and Hydru.s 'platyurus'X, extending the observations of Cantor 

 upon one of these, and I have lately brought forward some evi- 

 dence 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 lacunte 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 compara- 

 tively few species and genera. I am able considerably to extend 

 the knowledge of the occuiTence 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 lungs in a few Colubrine Snakes. I have already 

 referred to the lungs of certain Boidee §. 



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 i"ings. 

 These extremities are connected by a wide thin-Avalled 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 jDroper 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. 



Moi-eover, the cartilaginous semirings of the trachea are con- 

 tinued for a shoi't distance into the second and smaller lung. 

 The la,rge 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 lilje 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. 147. 

 X "Contributions to the Anatouiy of the Ophidia," ibid. 1906, vol. i. p. 41. 

 § Supra, p. 515. 



