218 MR. W. K. PARKER ON THE OSTEOLOGY 
fledgeling Heron (Ardea cinerea), the palatine part of the prevomer reaches to within an 
inch of the end of the beak, and the zygomatic part to within a quarter of an inch of the 
os quadratum,—its whole length being nearly 4 inches, the entire head at that time not 
being more than 5 inches 8 lines: compare this with the prevomer of the Amphibians ! 
The ‘‘ vomer ” of the Tinamou (Pl. XL. fig. 1) is full an inch long, and a line wide at 
the narrowest part ; in the Rhea (PI. XL. fig. 1, v.) it is more than 23 inches long and 
3 lines broad at the middle; the form is the same in both, and the relative size the same, 
but it is slenderest in the Tinamou. It forks in front in both, and these forks are 
underlain on each side by the palatine processes of the premaxillaries (Pl. XL. fig. 1, 
& Pl. XLII. fig. 1, v.pe.): in both cases it forms a splint-like sheath to the great 
basisphenoidal rostrum, which appears in front between and above the forks (Pl. XL. 
fig. 1, & Pl. XLII. fig. 1, r.bs.). How far this is from the structure of any gallina- 
ceous bird I need not say, where the vomer is extremely delicate and small, and the 
“‘ rostrum ” short (Pl. XXXVI. fig. 6.). 
In the Weka-Rail (Ocydromus) and in the Lapwing (Vanellus), the shorter “‘ rostrum ” 
lies in the vomerine groove (Pl. XXXVII. fig. 1, v.bs.) ; but it does not in either case 
reach the middle: still these birds have vomers and ‘‘ rostra”’ more in harmony with 
those of the struthious birds than the Fowls have. On one hand, the large, single, 
semicylindrical vomer of struthious birds comes near that of the mammals; on the 
other hand, it is unmistakeably like the single vomer of the Chelonians—having, like 
them, a broad anterior part on a lower plane than the rest and articulating with the 
premaxillz, a middle constricted part separating the middle nares from each other, and 
a posterior expanded part sheathing the cranio-facial axis, and articulating with the 
posterior end of the palatines and the anterior end of the pterygoids’ (Pl. XLII. 
fig. 1,v.). The posterior broad eud of the Tinamou’s vomer does not keep free as in 
the Great Ostriches, but agrees with that of the Apteryx in coalescing with the ptery- 
goids and palatines. It is very common for the vomer to keep distinct from the pala- 
tines in the Rails, Plovers, and in many both wading, swimming, and diving birds; but 
in a large number of the other great groups the posterior forks of the bone rapidly 
coalesce with the interior edge of each palatine, where they are sheathing the ‘‘ ros- 
trum.” But it is only, as a rule, in certain birds of a high and noble kind that we 
meet with a coalescence of the palatine elements to such a degree as to involve the 
pterygoids also. The Tinamou has this character; the Apteryx has it; and then we 
must pass to the three main divisions of the great typical group to find this state of 
things again. I have found this coalescence in the following birds :— 
* Amongst the typical birds, the Falcons (Falco), the Dicholophus, the Sacred Ibis (Threskiornis ethiopicus), 
some of the “ Meropidz,’’ the Wild Duck (Anas éoschas), and especially the Albatros (Diomedea exulans) 
come near the Chelonians in the condition of the vomer; in all these, however, the vomer is separated more or 
less from the palatines by the intervention of an additional segment on each side, viz. the “ mesopterygoids.” 
