OCR Text |
Show front of it-the thoracic lung is marked off from the tracheal by a short forwardly extending pouch of the former which lies dorsally, and therefore, as seen in dissection, beneath the lower end of the tracheal lung. Such a forward process of the thoracic lung is common in Snakes, but I have not found it in Coluber longissimus. It has in C. leopardinus obviously nothing to do with the tracheal lung. There is a second honeycombed and vascular rudimentary lung. In Coluber melanoleucus * there is a type of lung differing in many respects from that of the three species of Coluber already, or to be, dealt with. The trachea is continued down the lung for a very great distance. It is from high up in the neck an open gutter and runs as such to a point about half way down, or not far from the posterior end of, the liver. The trachea does not cease at the end of the vascular region of the lung, but extends some way beyond the point at which the lung ceases to be vascular. When a transverse section is made of the lung behind the heart, the appearances presented suggest at first that the trachea is quite independent of the lung. The elasticity of the cartilaginous rings keeps the trachea closed, and produces the impression of a closed tube running within the lung. It is not, however, closed but freely communicates along its whole length with the cavity of the lung. The lung-tissue does not extend forwards beyond the region of the heart; this species has therefore no tracheal lung. The honeycombed structure ceases in a very abrupt fashion along a line which is rather oblique. I found a pocket running forwards such as is met with in Coluber longissimus and is not uncommon among Snakes. There is a considerable distance in the neck-region between the separated extremities of the tracheal semirings. But the membrane which divides them is not swollen out into such a thin-walled sac as occurs in Coluber corais. It is rather thick, and nowhere could I find any traces of a honeycombed structure, which, considering the abrupt way in which the lung ends at the heart, would hardly be expected. Furthermore, there does not seem to be in this serpent any rudimentary left lung at all. If it be present, which I doubt, it is so small as to have escaped my observation. It is clear that Coluber melanoleucus presents more differences from the three species of Coluber that have been described than any of them do from each other. The absence of a rudiment of the left lungt, the enormous extension down the lung of the trachea, and finally the abrupt ending of the lung-tissue in the region of the heart, are the salient points of difference. I am much inclined to doubt whether the inclusion of this species in the same genus with the three species already referred to is, anatomically considered, a sound procedure. But I hope later to offer some observations upon the systematic arrangement of certain Ophidia. * I dissected two examples. f Even if this has been overlooked considerable differences remain Conp however, was unable to find it like myself. ' * 5 2 2 MR. F. E. BEDDARD ON THE VASCULAR AND [M a y 1 , |