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 axis; 

 the " Grallae," melting into " Palmipeds," form the secondary trunk'. 



In the Syrrhaptes the occipital plane (PI. 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 



' 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. ^ (^ 



