THE ANATOMY OF BIIWS. — OSTEOLOGY. 161 



The Facial Bones proper is the Vomer. — By " facial bones," as distinguished from 

 "cranial " bones, is meant the entire bony scaffolding of the upper and lower jaws, and of the 

 tongue, — parts developed in the pre-oral or maxillary, and first, second, and third post-oral, or 

 mandibular, hyoidean proper, and branchial, arches. 



The Vomer (Lat. vomer, a ploughshare ; figs. G2, 63, 75 to 80, v) is considered, by those 

 who hold the vertebral theory of the skull, to be the body of the foremost (fourth from behind 



— the basioccipital, basisphenoid, and presphenoid being the other threej cranial vertebra. So 

 far from having any such morphoh)gical significance, it is one of the late secondary bones, 

 developed, if at all, apart fi-om the general make-up of the skull, as a special superaddition 

 underlying the ethmoidal region, as the parasphenoid and basitemporal underlie the skull further 

 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 (Pterocletes) and bush quails 

 (Hemipodes) of the old world, and in certain of the true Gallince. 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 

 maxillo-palatines. Or, it may be united with separate ossifications, the septo-maxiUaries, 

 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 some- 

 times also with the pterygoid. Such is usually the fixture of the bone behind, and it then ridos 

 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 Passeiine group, which comprise the majority of recent 

 birds, is different fi-om this, the vomer being in front thickened, flattened and expanded laterally, 

 and connected wuth nasal cartilages and ossifications (alinasals and turbinals). Such a vomer, 

 deeply cleft behind to join the palatals, is endlessly diversified in the configuration of its fore end, 

 which may be notched, lobed, clubbed, etc. The general case of such a vomer is indicated by 

 the expression " vomer truncate in front," as distinguished from the simjily pointed or "spiked" 

 vomer. (For further details see description of the several patterns of palate-structure, beyond.) 



The Quadrate Bone (Lat. quadratus, squared; figs. 62; 63, n; 64, 65, 68, 69, 71, q_; 

 75, Qu), with which we may begin the jaw-bones proper, is the susijensorium of the lower jaw, 



— the perfectly constant and characteristic bone by means of which the mandible proper articu- 

 lates with the skull. Its rudiment is seen in the earUest embryos, at the corners of the pri- 

 mordial parachordal cartilages. It belongs to the mandibular (first post-oral) arch, of which it 

 is the proximal element. Its general morphology has caused much dispute. From the fact 

 that in birds one of its functions is to support, in part, the tympanum of the ear, it has been 

 identified with the tympanic bone of mammals, — that which in man fonns the bony tube of the 

 external auditory meatus. The view now generally accepted is, that the bird's quadrate repre- 



11 



