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Show 1889.] THE BODY-CAVITY IN LIZARDS, ETC. 453 Nothing appears to be known of the development of the subdivisions of the body-cavity in the Crocodile, and to treat the subject of this paper satisfactorily the writer should have a familiar and personal acquaintance with not only that, but with the whole corresponding course of development, in Mammal, Bird, and Lizard, so far as the partial or complete septa in the body-cavity are concerned. I have followed the development in the chick down to the twelfth day by means of complete series of consecutive sections taken in different planes, and particularly during the latter half of this period ; but I cannot pretend to an equal acquaintance with the development in Mammalia, and in common, as I believe, with other observers, I have not been able, in the case of the Lizards, to compare the development in Varanidce or Teiidee with that in Lacertidce. Nevertheless it may be well at the present stage to make known in a preliminary paper certain observed facts, and to indicate certain homologies which they suggest. I append a list of the more noticeable of the papers bearing on this subject to which I have referred ; but, while acknowledging indebtedness to the authors of the same, I do not attempt a resume of their contents ; but, except in those cases where reference is made to any of them, confine myself to sketching the facts from my own observation, and to stating the conclusions to which they appear to point. Certain subjects, such as the later stages in the development of the Avian diaphragm, and the formation of the air-sacs, as from the sixth to the twelfth day of incubation in the Fowl, and the relations and homologies of the various ligaments and septa about the liver-lobes in Birds and Reptiles, do not seem previously to have received full attention. The consideration of these and of certain other points seems to show that the complication of the membranes in the adult Bird and Crocodile can, to a greater extent than might be imagined, be analyzed and expressed in terms of structures found in other Reptiles, where the arrangement is simpler. II. ON THE SUBDIVISION OF THE BODY-CAVITY IN THE A D U L T FOWL. On carefully cutting away the sternum and ventral body-wall of a Duck or Fowl, we see that the liver-lobes for the most part lie in two sacs entirely shut off from the rest of the body-cavity (cf. Plates XLVIII. and XLIX. figs. 29 and 44-47, h, h! ; 1, 1'). These sacs are bounded ventrally by the sternum, externally by the vertical portion of the " oblique septum " of Huxley (s.ob.), mesially by the median ventral ligament (m) and posteriorly by the " omentum " (/3), which passes anteriorly into the hinder portion of a transverse septum (y) ventral to the abdominal air-sacs **. Not much, however, 1 Huxley appears to m e to have included this transverse septum (y) in his " oblique septum," while Perrault appears to have described the two elements /3 and y (just referred to separately, by reason of their arising quite separately in the embryo) as the " diaphragme transversal." Sappey (1, p. 35) says, speaking of |
