1889.] THE BODY-CAVITY IN LIZARDS, ETC. 4.53 



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 chiciv 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 1 believe, with otiier observers, I 

 have not been able, in the case of the Lizards, to compare the develop- 

 ment in Varanidce or I'eiidce with that in LacertidcB. 



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 tlie 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 tlie facts from my own 

 observation, and to stating the conclusions to which they appear to 

 pomt. 



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 rela- 

 tions and homologies of the various ligaments and se[)ta about the 

 liver-lobes in Birds and Reptiles, do not seem previously to have 

 received full attention. 



Tlie 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 Adult 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'). Tiiese sacs 

 are bounded ventrally by the sternum, externally by the vertical 

 portion of the " oblique septum " of Huxley {s.oh.), mesially by tlie 

 median ventral ligament (»i) 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, 



' Huxley appears to me to have included this transverse septum (y) in his 

 " oblique septum," -while Perrault appears to have described the two elements /j 

 and y (just referred to separately, by reason of their arising quite separately in 

 the embryo) as the " diajthragme transversal." Sappey (1, p. 35) says, speaking of 



