388 PROFESSOR OWEN ON THE GENUS DINORNIS. 
the thickness, especially the depth, of the wall of the ring. The extreme of the latter, 
or breadth in the axis of the windpipe, is 3 lines, as at fig. 2, 6, Pl. XLVII.; but this is 
partial, the hoop decreasing to 2 lines and 13 line at part of the circumference, in a 
few at the small ends of the ellipse, or the lateral parts of the hoop; the more common 
breadth is from 2 lines to 14 line (Pl. XLVII. fig. 1, d); those found at the base of the 
skull, and inferred to be from the upper part of the windpipe, were 1 line, decreasing 
partially to 4 a line, in depth. There is less range of thickness in the elliptical rings 
of Dinornis crassus, as, e.g. from =’ to $ of a line, seldom getting to % (ib. figs. 1 & 3). 
There is a certain range of size and of shape of the ellipse: thus, in fig. 1, a, 6, excep- 
tional instances of subcircular rings are figured; in fig. 3, a, 6, the long axis is 10 lines, 
the short one 9 lines; in fig. 3, ¢, the long axis is 11} lines, the short one 8 lines. Most 
of the rings have intermediate proportions; in a few the ellipse is less regular, one side 
inclining to flatness. There is a variety also in the configuration of the surfaces of the 
hoop; instead of the outer surface being convex from the upper to the lower margins, 
as in the slender rings detached from beneath the skull, it is flat, especially in the 
broader varieties, in which the inner surface preserves a slight convexity in the same 
course; in some rings the outer surface is slightly concave from edge to edge (as in 
fig. 2, d). 
Of the tracheal rings referred to Dinornis crassus some are preserved in groups, 
cemented in their consecutive arrangement upon and by the matrix. These groups 
include one of seven rings (fig. 4), two of six rings, one of five rings (fig. 5), two of four 
rings with part of a fifth (fig. 6), as many of three rings, and more of two rings so kept 
in natural sequence. In three instances of the ‘“‘ two rings” these show broader and 
narrower parts of the outer surface, alternating, the extremes being at the small ends 
of the ellipse, or at the sides of the tube. This character has been noted in recent 
birds, especially in the Waders’, the appearance being that presented by the tracheal 
rings of the present extinct Moa (fig. 7, @,4,¢); but the analogy of Apteryx (antea, 
p- 386) led me to test the relation of the appearance to reality. 
Succeeding in working out the cementing matrix in one instance, and exposing the 
inner surfaces of the two interlocked rings, I found, as I had anticipated, that the outward 
appearance was due in some degree to intussusception, the inner surface being broader 
where the outer surface was narrower, and vice versd. Nevertheless a slight inequality 
of breadth is shown in some detached rings at the ends of the ellipse; and it may 
indicate that they come from a part of the windpipe situated where it was subject to 
most flexure in the bendings of the bird’s neck. 
‘ «They are alternately narrower at certain parts of their circumference and broader at others; and in these 
cases the rings are closely approximated, as it were interlocked. This structure is most common in the Gral- 
latores, where the rings are broadest alternately on the right and left sides.” —Anat. of Vertebrates, ii. p. 219. 
