468 MR. G. W. BUTLER ON THE SUBDIVISION OF [Nov. 19, 
the case of Birds and Mammals), I give for what it may be worth 
the following interpretation, based mainly on the study of very young 
specimens either recently hatched or still within the egg. I have 
examined but one well-preserved adult specimen (of the Alligator 
type), and some eight or more small animals, four of which were 
unhatched, three of them not having yet cut their teeth, and being 
possessed of the horny egg-breaker on the snout. 
Young animals such as these are, I think, best for making out 
the relations, as not only is it easy to cut longitudiual and transverse 
sections of them, but in the adult the true relations of the 
membranes tend to become obscured by adhesions or other adaptive 
changes, and the only drawback is the caution necessitated by the 
delicacy of their membranes. 
That which first strikes the observer with regard to the body- 
cavity of a Crocodile, is the subdivision of the Pleuro-peritoneal 
cavity into Pulmohepatic and Intestinal portions by a post-hepatic 
septum; secondly, the facts mentioned by Huxley (4, p. 568), that 
the gizzard is firmly connected with the body-wall, so that it appears 
to be itself shut off from the intestinal cavity ; and that the liver 
projects into a number of different sacs *. 
In these three points the Crocodiles at first sight approach the 
Birds rather than other Sauropsida. It appears to me, however, 
that the Crocodiles, in the matter of the subdivision of their body- 
cavity, are distinctly reptilian rather than avian; and that the only 
satisfactory way of comparing the two types, in the absence of the 
much needed embryological data (cf. supra, p. 453), is to analyze 
the complex condition of each into its component elements, and to 
compare these in the light of our knowledge of the simpler Saurop- 
sida (Lacertilia), and of the development of the bird. 
Fig. 35 represents one of the young Crocodiles referred to 
reduced one half, the lines indicating the approximate planes of the 
sections sketched in the corresponding figures, which are on a scale 
three times as large *. 
Fig. 42 is intended to show the cut edges of the pleuro-peritoneal 
membrane, as they would appear on the removal of the ventral body- 
1 Hunter in ‘Essays and Observations on Natural History...... ’ (edited by 
Owen), vol. ii. pp. 886 & 337, gives a careful account of the relations and 
attachments of the liver in theadult Crocodile. He emphasizes the fact that the 
liver is shut off from the abdominal cavity, and says that it itself makes a kind of 
diaphragm. He adds, however, that on account of the well-marked character 
of the membranous lamella belind it, we may “consider the liver as in the 
thorax.” 
2 Of. Owen, P. Z.8. 1831, pp. 137 and 169. I was not aware, until after the 
present paper was in type, that this author had described some of the anato- 
mical features herein discussed. 
3 The longitudinal sections in question, figs. 39, 40, & 41, are drawn from the 
ventral side, as are also figs, 42 & 438, and also fig. 29 of the duck, and 31 of 
Tupinambis, All these differ from the horizontal sections of the developing 
bird, which are drawn from the dorsal side. This difference being once noted, 
I hope that there will be no difficulty in making any comparisons that may be 
desired. The transverse sections of the Crocodile, figs. 36, 37, & 38, agree with 
those of the developing bird, and also with figs. 45 & 47 of the adult, and 32 of 
Tupinambis, in being drawn from behind. 
