PROFESSOR OWEN ON THE GENUS DINORNIS. 385 
fibrous kind, expands, ascends, and arches inward over the great ganglion, becoming 
thinner as it approaches the median line, where it descends in contact with the corre- 
sponding part of the opposite hemisphere as a thin film forming the inner or median 
and the posterior wall of the “lateral ventricle” (Pl. XLV. figs. 7 & 8,a"). This is 
exposed by a longitudinal section of the thicker part of the roof (q' in fig. 5, and in 
Pl. XLVI. fig. 2), the smooth ventricular surface of the ganglion being shown at 2. 
In Pl. XLV. fig. 7, the thin inner wall of the ventricle (a) is exposed by removal of 
the “corpus striatum” and the thicker part of the ventricular wall (fig. 5, a’). The 
“ corpus striatum” is impressed by equidistant transverse vascular linear grooves. 
Figure 10 shows a vertical transverse section of the hemispheres, where they are 
united by the “anterior commissure” (0): the depth of the interhemispheral fissure ( p) 
is seen below the commissure; and the shape of the section of the ventricular cavity is 
shown at g. A similar section, 3 lines in advance (fig. 9), shows the ventricle (q) 
shrunk to the under and inner surfaces of the hemisphere. The section across the base 
of the rhinencephalon (fig. 8) exposes the continuation of the ventricle (q) into that fore- 
most primary division of the brain. 
The rhinencephalon (figs, 1 & 2, 7) is as remarkable in the present singular bird for its 
large size as is the mesencephalon (fig. 5, )) for the smallness of its principal elements. 
The mammalian proportions of the rhinencephalon (figs. 3, 4, 7) involves the develop- 
ment of the fore part of the prosencephalon, including those continuations of fasciculi 
of white with grey matter forming the “crura rhinencephali,” the homologues of what 
are described in Anthropotomy as the “roots of the olfactory nerves.” It is that which 
gives rise to the semblance of “anterior lobes” of the hemispheres on the upper surface 
of the brain of the Apteryx (fig. 2,@), and to the tumid tracts below continuing the 
hemispheres in advance of the chiasma and its minute optic nerves (figs. 3 & 4, aa). 
The prosencephala (fig. 1,@) overhang about two-thirds of the rhinencephala (ib. 7). 
One may distinguish at the under part of the hemispheres an outer and an inner 
division of the “crura rhinencephali” (ib. 7’) by feeble degrees of prominence; but they 
are not divided, as in Mammals, by a “ perforate tract,’ or by the definite superficial 
fascicle of white fibres. 
§ 3. Cerebral nerves of Apteryx. 
The rhinencephala occupy special compartments or fosse at the fore end of the 
cranial cavity. ‘The olfactory nerves (Pl. XLV. fig. 2,s) perforate the anterior and 
inferior wall of the rhinencephalic chamber by several foramina, but are closely 
invested and united by the neurilemma, especially along their upper surface, so as to 
appear, for an extent of 8 or 9 lines, each as one large olfactory nerve. From 
the underpart of these fasciculi, filaments pass down to the broad ethmoturbinals 
(fig. 1, ae); the rest of the nerves are dispersed upon the septum narium and the middle 
turbinals (ib. a), which seem to prolong forward and to make one huge mass with 
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