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§ 7. Trachea of Dinornis ingens? 
About 70 tracheal rings show an average of size and shape as in that of fig. 17,a,4,¢; 
the extremes in regard to depth of hoop, in this series, are given in figs. 19 & 20. The 
bone, in all, is of unequal thickness, longitudinally rugose, but unequally so, on the 
outer surface, smooth within (fig. 18, longitudinal section). On the rougher part of the 
ring the bony substance stands out in the form of granules or ridges, the latter running 
in the direction from one margin to the other (figs. 19 & 20, 6,4). These margins 
(figs. 17 & 19, a) are flat or “truncate,” as in the smaller rings (figs, 13-15, a) of the 
present robust type; but here the margin is more uneven, with risings and depressions, 
somewhat irregular, but on the whole at right angles to the outer and inner surfaces. 
In this series were specimens of two partially confluent rings, or of a broad hoop 
twisted upon itself spirally, so as to simulate two hoops, Of these specimens one is 
represented at fig. 21, a, 4, a second at fig. 22; fig. 23 shows more plainly a partial con- 
fluence of the two bony rings. Seven rings of the average size of those provisionally 
attributed to Dinornis ingens (Pl. XCII. fig. 6) occupy an extent of the trachea 
equalling that which includes thirty-nine in Caswarius galeatus (ib. fig. 5). 
§ 8. Trachea of Dinornis robustus ? 
I have finally to notice the largest specimens in the present collection, which ex- 
emplify the most extraordinary degrees of thickness and strength of bone which have 
been hitherto observed in the windpipes of Birds. 
I think it not improbable that an osseous hoop like that represented in Pl. XCIII. 
fig. 24, a, b, might, if received as a solitary fossil, have passed rather for a section of the 
shaft of a pneumatic limb-bone, being as large, for example, as such section of the femur 
of a Cassowary, but thicker in the walls. He must have been a bold, as well as acute, 
paleontologist who would have pronounced it one of the rings of a bird’s windpipe. 
I have now, howeyer, received upwards of thirty specimens, averaging the dimensions 
of that of fig. 24. They are, most of them, rather more elliptical, less circular, than 
the smaller hoops of a like type (figs. 17-23). ‘The long diameter averages, as in fig, 24, 
1 inch 2 lines, the short diameter 1 inch, outside measure; the area, which is a more 
regular ellipse, gives 104 lines and 9 lines in the two diameters. ‘The breadth, or we 
may now say the length, of the hoop’s wall, 7. ¢. from the upper to the lower margin, 
averages 9 lines and 74 lines, not being uniform all round; the difference of thickness 
is greater, viz. from 22 lines to $ a line (fig. 24, a, and fig. 32). 
The contrast between the outer and the inner surfaces of the tracheal hoops in 
Dinornis becomes greater as these increase in size. In the present series, which may 
belong to Dinornis robustus, the irregular longitudinal striation prevails over the 
external surface of the bone; but there are other characters. 
At one or two parts of the circumference a part of that surface (figs. 24, 26, 28, x ) pro- 
jects beyond the rest, usually from the middle third part between the upper and lower 
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