OF GALLINACEOUS BIRDS AND TINAMOUS. 191 
forking: at the extremities of the twigs we cease tracing, and if we would run up 
another branch we must return to the forks and begin our work from an old point. 
The exuberant life at the base of the bird-tree yields us the inordinately large Ostriches ; 
just at the first fork of the main axis we have the Tinamous; the tree branches, and 
we have the Sandplover and the Hemipodius ; then its repeated forkings and trifurcations 
yield us the Pigeon, the Plover, and the Fowl. Each true typical group has its 
culminating forms, ‘‘ and there an end.” These may culminate near the base as side- 
branches, or at the top, and there we have the fullest exhibition of bird-qualities 
combined with large size. In the very heart of this tree are the countless typical 
groups of birds that, as it were, fork and refork, overlap and intertwine themselves. 
Where the Plover-type has separated from the Tinamous, Sandgrouse, and Hemipodii, 
there we have a great division made, as is now and then seen in the Silver-fir, a great 
branch taking the character of a second but smaller leader, and the tree is in a sense 
double; so the bird-tree becomes double from that point. The land-birds proper, or 
walking birds, as they run up into the perchers and climbers, form the great true azis ; 
the ‘‘ Grallz,” melting into ‘‘ Palmipeds,” form the secondary trunk’. 
In the Syrrhaptes the occipital plane (Pl. XXXVI. figs. 1,3, & 4) is not quite so low 
as in the Pigeon, but it forms a more obtuse angle with the basicranial axis than in the 
Lapwing (Vanellus): this is at once a strongly differentiating character from the Grouse, 
where that angle is a right angle. Yet it is in the Hemipodii that we have the nearest 
approximation to the Pigeons in respect of the middle fontanelle: this may be transient 
in the Syrrhaptes ; but there is no trace of it in the adult bird, which agrees in this with 
the Grouse and the Ostriches. But the occipital plane, save for this character, is 
exceedingly like that of the smaller Pigeons; and the texture of the entire skull and 
face agrees much more closely with the Pigeon than with any other bird. The 
foramen magnum (fig. 1) is large, and is intermediate between that of the Lapwing and 
the Pigeon: in the latter bird and in the Ptarmigan the upper outline is a very perfect 
semicircle, but in the Lapwing it is a slightly rounded right angle; in the Syrrhaptes 
it is exactly intermediate. Again, the occipital condyle is a beautiful hemispherical 
knob in the Lapwing, only a faint dimple existing at its posterior edge ; in the Grouse 
it is kidney-shaped, the dimple forming the large concave “‘hilum;” in the Pigeon 
the ‘hilum ” is shallow; whilst, finally, in the Syrrhaptes it is nearly as faint as in 
the Lapwing. In the Grouse the condyle is transverse; in the other three the axial 
diameter is slightly the longest. The tympanic wings of the lateral occipital are 
scarcely more outspread in the Syrrhaptes and the Pigeon than in the Ostrich and the 
Plover ; in the true Grouse their extraordinary development yields an excellent character 
by which to distinguish them as a subtype from the typical Fowls. 
The skull of the Syrrhaptes, seen endwise (fig. 3), shows in its narrowness upwards a 
1 This fanciful comparison has rather a mnemonic than a scientific value. If the higher birds have descended 
from generalized forefathers, such as the Ostriches, yet there must have been several such ancestral groups. 
VOL. V.— PART III. 2c 
