36 
foramen is present in both specimens, as in the one originally described (Proc. Zool. 
Soc. part xvi. p. 2). This foramen also exists in Owls and Parrots, but not in all Pigeons ; 
the JDidwnculus (PI. III. fig. 2) shows no trace of it; I have also failed to find it in the 
skull of a Crown-pigeon ( Goura coronata). The superoccipital ridge is defined by the 
subsidence of the surface beneath it being continued directly from the upper, almost 
flat, smooth surface of the cranium : the middle part of the ridge is more produced than 
the angles. In the great breadth of the occipital surface compared with its depth, in 
its flatness from side to side, and its aspect backward and a little upward, Bidus most 
resembles Binornis. The basioccipital curves downward, and unites with the basi- 
sphenoid in developing the pair of larger tuberosities (PI. XI. fig. I, 5), which ter- 
minate about ^ an inch below the occipital condyle. There is nothing of this structure 
in the Columbine cranium. In one of my Dodo’s skulls there is a pair of small 
tubercles between the larger basioccipital ones ; these are not developed in the other 
cranium. The basisphenoid is subquadrate, and flattish below, impressed by a shallow 
median longitudinal channel. 
The hypoglossal nerve escapes by two small foramina on each side of the base of the 
condyle ; external to these is the vagal foramen ; still more external is the depression 
(ib. a) perforated below by the entocarotid, glossopharyngeal, and sympathetic, above 
by the tympanic vein. The entocarotid canal opens into the hind part of the sella or 
pituitary fossa : the vagal canal begins within the skull, above the hypoglossal foramina. 
The paroccipital carries the posterior surface of the skull downward and outward to a 
much greater degree than in any Dove, but to a less degree than in Binornis. The 
Eustachian tubes impress the outer and fore part of the basisphenoid. 
The temporal fossse (PI. III.), in the present specimens, show the same contraction in 
proportion to their depth by which the original skull of the Dodo, compared with that 
of the Binornis, ‘ Proc. Zool. Soc.’ (1848, p. 3), difiered from the larger extinct wingless 
bird. In the approximation of the postorbital process to the mastoid, Bidunculus shows a 
closer resemblance to Bidus than does Goura, in which the temporal fossa, besides being 
narrow, is shallow. The temporal muscle appears to spread its origin above the fossa 
upon the sides of the cranium, forward half an inch in advance of the postfrontal 
process, and backward to the outer angle of the superoccipital ridge. 
The parietal region is broad, flat, and short, as in Binornis, not convex as in Doves ; 
it is also impressed at its middle part by a shallow transverse groove, continued out- 
ward and forward of less depth and definition, so as to mark off the convex interorbital 
part of the swollen frontals. 
The outer side of the mastoid is convex, smooth, overhanging the tympanic cavity, 
and sending off a short process, the base of which is defined in one cranium by a trans- 
verse ridge in front of the anterior articular cup for the tympanic bone. A similar 
process is developed in Bidunculus, not in Goura, where it is barely indicated. 
The presphenoid is compressed, but thickened and rounded below, where the pala- 
