386 PROFESSOR OWEN ON THE GENUS DINORNIS. 
longitudinal tract (a), next the mid line, is divided from the outer part of the hemi- 
spheres ; and this is partially subdivided into a posterior (@’) and anterior (a’) portion by 
a shallow depression answering to the “ Sylvian fissure.” 
The optic lobes (figs. 11, 12, 13, 4, 4) are, relatively as well as absolutely, larger than 
in Apteryx, corresponding with the indications, given by the orbits or bony beds, of the 
larger and better-developed organs of vision in Dinornis, the species of which we may 
conclude to have been diurnal; they are visible in the upper view (fig. 12, 4, 4) as well 
as in the side view (fig. 11). 
No demarcation of a “pons” can be satisfactorily traced on the cast; but the tri- 
geminal swelling is plain. The length of the macromyelon is 11 lines, its breadth is 
9 lines. 
The cerebellum shows a pair of low lateral lobes (fig. 11, c’) at its fore part, and 
behind this the depression answering to the upper semicircular canal. The length of 
the cerebellum is 1 inch 2 lines, its breadth at the lateral lobes is linch. The vertical 
diameter of the epencephalon (ib. ¢, d) is 1 inch 4 lines; the breadth of the mesence- 
phalon (fig. 15, 7, 4), taken outside of the optic lobes, is 1 inch; the length to the fore 
part of the chiasma is 8 lines; each optic nerve (¢) has a thickness of 2 lines. The breadth 
of the cerebrum (fig. 12, a, a’) is 2 inches 2 lines; its length is 1 inch 7 lines; its depth, 
or vertical diameter, is 1 inch 1 line. The breadth of the rhinencephalon (7) is 8 lines; 
the length of each lobe in advance of the cerebral hemisphere is 24 lines. They are 
relatively less than in Apteryx. 
The hypophysis, as represented by the cast of the “sella” (figs. 11, 13, y) is of con- 
siderable size; there is an indication of a better-developed pineal gland (fig. 12, p) 
than in the Apterya. 
) 6. Trachea of Apteryx, Struthio, and Casuarius. 
In the Apteryx australis the trachea has a nearly uniform diameter throughout its 
extent; the rings, from 120 to 150 in number, are entire and cartilaginous. When the 
windpipe is relaxed the rings alternately overlap, and are overlapped by, each other at 
their sides, appearing to be alternately narrower on one side than on the other; but when 
the tube is stretched this appearance is lost, though not wholly, the rings then showing 
a slight difference of breadth in the axis of the tube at their sides. They become 
gradually smaller in circumference and diameter in the last twenty, which are less 
closely attached together than in the Ostrich and Emu. 
In the trachea of the Cassowary, for the opportunity of examining which I am 
indebted to Dr. Murie, the rings, mostly entire as in other birds, vary in depth, @.e. in 
the diameter of the hoop parallel with the length of the tube, and they correspondingly 
vary in thickness (Pl. XLVI. fig.5). Their excess in these diameters is shown at about 
one-fourth down the trachea; they become narrowest and thinnest at the terminal tenth 
part of the tube, where a solution of continuity of the ring begins to show itself along 
