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 (Chamcsopelia passerina) (PI. 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) (PI. XXXVI. fig. 8) and in the Lapwing (Vanellus) (PI. XXXVII. 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 " Gallinae " have opake, thick-walled skulls (especially the 

 typical species ; for they are still opake, but thinner, in the " Tetraonidse ") , in the 

 Pigeons, as in other arboreal birds, the walls are thin and translucent, and the diploe 

 very delicate. 



In the Plovers and their allies the bone is much less opake than in the Gallinaceous 

 birds ; but the diploe, instead of being extremely thick, as in them and in the 

 " Struthionidse," 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 diploe, 

 as well as in the smooth, polished condition of the surface, agrees with the " Columbidse." 

 Looking at the skull of the Hemipodius from above (PI. XXXIV. fig. 3, PI. 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 Coturnix. 



In Chamceopelia, 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 Chamceopelia 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 (Pis. 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 (PI. 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 



