RESPIRATORY SPACES OF THE LUNGS 365 
of the septum of the secondary order always have their origin 
in those of the first order, and similarly those of the third order 
are derived from the secondary. The manner of the interweaving 
of the muscle bundles in the free edges of the septa is similar to 
that of the tortoise, but, as it is not conspicuous here, it will be 
described later. In all other particulars my findings agree with 
Gaupp’s descriptions. 
Megalobatrachus japonicus. Before I proceed to a statement 
of muscle fibers, I will describe briefly the septa. The free edges 
of the primary septa are somewhat flattened and are perpendic- 
ular to the septa themselves, so that in transverse section they 
appear as T-shaped structures. The free edges of the secondary 
and tertiary septa are on the contrary not flat, but club-shaped 
Gf seen in sections). The free edges of the secondary septa always 
arise from the inferior surface of the primary septa and take a 
concave course. ‘The free edges of the tertiary septa pursue a 
similar course but arise from those of the secondary. The muscle 
fibers are well developed in the free edges, as in Rana. ‘The 
muscle bundles of the free edges of the primary septa are strongest 
and flattened. Those of the other septa are less strong according 
to the order of their position. 
The free edges of the septa come together from three or from 
as many as ten directions, sometimes even more. From this it 
will be seen that the muscle bundles must of necessity be inter- 
woven with each other in a great number of ways. Several 
instances of this are given in the next diagram. Figures 19 and 
20 show the muscle bundles of four free edges; figures 21 and 22, 
of eight free edges coming together at one point. The muscle 
bundle of any free edge passes in most cases to two different free 
edges. Figure 23 shows the muscle bundle of a free edge passing 
to the free edge of an adjacent septum, and particularly encir- 
cling the passage into the respiratory space. 
The muscle bundles, which have their origin in the muscle 
tissue of the free edges, run in the septa and unite ultimately with 
those of the outer lung wall. The muscle fibers of the lung of 
Megalobatrachus generally form bundles. Though the muscle 
fibers of Rana nigromaculata form bundles, they also may be seen 
running singly or in groups of a few fibers, 
