238 GENERAL ORNITHOLOGY part ii 



it is one of the late secondary bones, developed, if at all, apart from 

 the general make-up of the skull, as a special superaddition under- 

 lying the ethmoidal region, as the parasphenoid and basitemporal 

 underlie the skull farther back. Its character is extremely variable 

 in the class of birds, though usually constant in the several natural 

 divisions of the class, — a fact which confers high zoological value 

 upon this anomalous bone. A vomer is a symmetrical mid-line 

 bone of the base of the skull, found if at all at or near the end of 

 the rostrum. It is originally double, i.e.. of right and left paired 

 halves. These halves persist distinct in the woodpeckers, and are 

 remote from each other, one on each side of the mid-line (Fig. 80). 

 The vomer is wanting entirely in the Columbine birds, as the 

 pigeons and some of their allies, as the sand-grouse {Pteroclidce) and 

 bush-quaUs (Hemipodiidce) of the old world, and in certain of the 

 true Gallinm. Its connections are various. It may be borne free 

 upon the end of the rostrum. It may be applied like a splint by 

 a grooved upper surface to the under side of the rostrum, and so 

 fixed there ; or, in such situation, it may glide along the rostrum 

 according to the movements of the palatal parts with which it may 

 connect. Thus, in the ostrich (Fig. 75), it saddles the rostrum 

 below, and is joined by the maxillopalatines. Or, it may be united 

 with separate ossifications, the septomaxillaries, which in some birds 

 bridge across the palate (Fig. 80). The commonest case is its deep 

 bifurcation behind (Fig. 79), each fork uniting with the palate bone 

 of its own side, and sometimes also with the pterygoid. Such is 

 usually the fixture of the bone behind, and it then rides along as 

 well as simply bestrides the rostrum. The anterior end of the 

 vomer may be perfectly free, projecting into the floor of the nasal 

 chambers (Figs. 62, 77), or the fore end may be variously steadied 

 or connected with maxillary processes (Fig. 78). When free in 

 front, and often when not, the vomer is a simple share-like plate, 

 more or less expanded vertically, quite thin laterally, and " spiked," 

 i.e. running forward to a point; under these circumstances it may 

 or may not bifurcate behind, and be there attached to the palatines 

 or not. But the commonest case of vomer, shown by the great 

 Passerine group, which comprise the majority of recent birds, is 

 difierent from this, the vomer being in front thickened, flattened 

 and expanded laterally, and connected with nasal cartilages and 

 ossifications (alinasals and turbinals). Such a vomer, deeply cleft 

 behind to join the palatals, is endlessly diversified in the configura- 

 tion of its fore end, which may be notched, lobbed, clubbed, etc. 

 HhQ .general' case of such a vomer is indicated by the expression 

 " vomer truncate in front," as distinguished from the simply pointed 

 or "spiked" vomer. (For further details see description of the 

 several patterns of palatal structure, beyond.) 



