460 MR. G. W. BUTLER.ON THE SUBDIVISION OF [Nov. 19, 
named the ‘recessus superior sacci omenti” in Mammalia, whose 
homologues in the Bird are much more conspicuous, that it occurred 
to me that these recesses and their bounding walls might serve as 
landmarks, and enable us more definitely to contrast the diaphrag- 
matic structures in the two classes (¢f. infra). 
III. (c). On the Development of the Pulmohepatic Ligaments and 
Recesses. 
In this connexion it will be convenient to consider the develop- 
mental changes in the chick classed under head (D) on p. 456. 
Referring to figures 1—4 (of which 1 and 2 are transverse sections 
of a 6th-day chick, 3 of an embryo of Lacerta vivipara, 4 of an 
embryo mammal’), we see running down the centre of the sections 
the median vertical sheet of tissue (m) which in all the types under 
consideration forms a complete vertical septum in the thoracic and 
anterior abdominal regions. On either side of it are set the lungs 
and the two halves of the liver, while the alimentary canal runs in 
its midst. 
It will further be noted that in all three cases the right liver-lobe 
is attached to the lung of its own side by a vertical ligament 
(«), which closes on the outside a space (2). The latter is blind 
anteriorly and opens into the general peritoneal cavity behind. 
In fig. 1, which is a section anterior to fig. 2, we see that in the 
chick there is, on the left side also, a corresponding ligament (a) 
and included recess (2'), while in the case of the Mammal and (in 
this instance) of the Lizard there is no such ligament traceable on 
the left side, and therefore no recess, properly speaking, though 2’ in 
figs. 3 and 4 marks where it should be. Now the recess on the 
right side (2) is the ‘‘ recessus superior sacci omenti’’ of His, as 
quoted by Ravn (9, p. 141), and the ligaments (a) are those which 
in the Bird can be clearly traced developing into the pulmohepatic 
ligaments ; while the recesses, with the addition on the right side of 
all that remains of the omental sac proper, develop into the 
pulmohepatic recesses, 
According to Ravn (op. cit. figs. 15, 16, and text) this ‘‘ recess” 
on the right side is continuous with the main omental sac as late as 
about the 15th day in the Rabbit, but by the 17th day (p. 146) it 
has become constricted off from the latter cavity and persists as a 
separate closed peritoneal sac, which comes to wrap round the 
cesophagus. 
By a reference to the Plates, the development, in the chick, of 
these pulmohepatic recesses and ligaments may be followed. Figs. 
1 and 2 are transverse sections of the 6th day (and the relations are 
much the same even on the 4th day). Figs. 5, 6, 7 may be 
called transverso-longitudinal sections (cf. fig. 25) of a 7th day 
embryo. Of these fig. 6 shows the foramen of Winslow (f. WV.) 
leading from the main peritoneal cavity into the sac (2) of the right 
side, part of which corresponds to the omental sac of Mammals, 
1 See also figs. 6-9, 11, 12, 14-18 of Ravn’s paper (9). 
