174 MR. W. K. PARKER ON THE OSTEOLOGY 
for some distance at its highest part. This sinus becomes entirely enclosed in bone 
just at the centre of each superoccipital piece, and emerges as a vein, to join the veins 
of the neck, close above the junction of the superoccipital with the lateral element. 
There is a great variety, however, in the manner in which this vein is enclosed ; for in 
the feeble skull of the Ground-Pigeon (Chameopelia passerina) (Pl. XXXIV. fig. 7) it 
soon finds the surface, but in Columba palumbus it burrows much further downwards 
in the skull-wall before it escapes. 
This vein is very small in Hemipodius, and is much enclosed in bone; in the Grouse 
(Lagopus) (Pl. XXXVI. fig. 8) and in the Lapwing (Vanellus) (Pl. XX XVII. fig. 2) it is 
as large as in the Pigeon—the degree of its concealment in the bone, as in the latter bird, 
depending upon the age of the individual. The condition of the bone itself is very 
instructive ; for ‘whilst the ‘‘ Galline ”’ have opake, thick-walled skulls (especially the 
typical species ; for they are still opake, but thinner, in the ‘‘ Tetraonide”’), in the 
Pigeons, as in other arboreal birds, the walls are thin and translucent, and the diploé 
very delicate. 
In the Plovers and their allies the bone is much less opake than in the Gallinaceous 
birds; but the diploé, instead of being extremely thick, as in them and in the 
« Struthionide,” is very deficient. This latter condition of the bone coexists with an 
increasing fattiness of the bone as we pass from the Plovers, through intermediate forms, 
to the plunging and diving ‘‘ Palmipeds.” 
In Hemipodius the skull-wall, in its transparency and in the delicacy of its diploé, 
as well as in the smooth, polished condition of the surface, agrees with the ‘‘ Columbide.” 
Looking at the skull of the Hemipodius from above (Pl. XXXIV. fig.3, Pl. XXXV. 
fig. 3), and seeing how the frontals are narrowed between the orbits, one might be 
beguiled into the opinion that it was but little modified from that of Coturnia. 
In Chame@opelia, however, this region is not much wider across than in the Quail and 
the Hemipodius ; yet as we pass to the Ringdove (C. palumbus), and especially to the 
Dodo, we see to what a width this part may grow. 
What the Dodo is to the Chame@opelia in this respect, that the Adjutant is to the 
Bittern ; and the same remark holds good with regard to the interorbital septum also. 
It is well to be aware of the great amount of modification due merely to the necessities 
of a gigantic organism, and in no way affecting our conclusions concerning matters of 
affinity (see ‘ Ibis,’ July 1862). 
There is a shallow sagittal fossa in the Hemipodii ; that is to say, the frontals incline 
gently towards each other, as is very common in small birds (Pls. XXXIV. & XXXV. 
fig.3). In H. varius the long-oval elevations on each side the sagittal line, on the main 
part of the frontals, are very distinct and large; they are very indistinct in the smaller 
species (Pl. XXXIV. fig. 3). They exist in many birds, especially small forms, where 
the convexities of the prosencephalon affect the outer table through the inner. 
The rim of the orbit, although projecting but little, is perfect for nearly three-fourths 
