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the inner surface, and the denser character of the osseous texture at the thicker part 
of the wall of some of the rings. 
§ 9. Trachea of Aptornis defossor. 
With a sternum, pelvis, and some other parts of the skeleton of Aptornis defossor, 
more entire than those described in my Memoir No. XV., and subsequently received, 
were a few rings of the trachea, of elliptical shape, averaging 7 lines and 5 lines in the 
two diameters (Pl. XCII. fig. 7), with a depth of the hoop of 1} line. These rings show 
a pair of narrow notches, one at the upper, the other at the lower margin, at opposite 
sides of the hoop, at its shorter diameter (ib. a,c). In the instance of two of these rings 
in connexion, the partial and reciprocal overlapping or intussusception was defined by 
or took place at these notches (ib. 0). 
