assembly. Desmognathae (fig. 5) were supposed to have the maxillo-palatines united across the middle line, either directly or by the intermediation of ossifications in the nasal septum. This is a hopeless assembly. Parker and Fürbringer have demonstrated that desmognathism has been produced in half a dozen ways, implying numerous cases of convergence without any nearer relationship than that they are all derived from some schizognathous group or other. The Aegithognathae, meant to comprise the passeres, woodpeckers and swifts, &c., are really schizognathous but with a vomer which is broadly truncated in front.
The remainder of the appendicular skeleton (fig. 6) of the head requires little description. The maxillaries are connected with the distal anterior corner of the quadrate by the thin, splint-like jugal and quadratojugal. The quadrate is invariably a conspicuous bone and movably articulating with the cranium and by a special process with the pterygoid. The mandible is composed of several bones as in reptiles. The os articulare bears on its inner side the inner mandibular process which serves for the insertion of part of the digastric muscle or opener of the mouth; another portion of this muscle is attached to the os angulare, which frequently forms a posterior mandibular process. The greater part of the under-jaw is formed by the right and left dentaries, which in all recent birds are fused together in front. Supra-angular and coronoid splint-bones serve for the insertion of part of the temporal or masseter muscle. Additional splints rest on the inner side of the jaw. Like the crocodiles, birds possess a siphonium, i.e. a membranous, or ossified, tube which rises from a pneumatic foramen in the os articulare, on the median side of the articulation, and passes upwards between the quadrate and lateral occipital bone, opening into the cavity of the middle ear.
|Fig. 6.—Skull of adult Fowl. Here the temporal fossa is bridged over by|
the junction of the post-frontal and squamosal processes (pf., sq.). The
processes of the mandible (iap, pap) are characteristic of this type, and
of the anseres.
|a, Angular of mandible.||pa, Palatine.|
|ar, Articular.||pap, Posterior angular process of mandible.|
|bt, Basi-temporal.||pe, Ethmoid.|
|d, Dentary.||pf, Post-frontal.|
|eo, Lateral occipital.||pg, Pterygoid.|
|eth, Ethmoid.||ps, Pre-sphenoid.|
|f, Frontal.||px, Premaxilla.|
|iap, Interangular process of mandible.||q, Quadrate.|
|ios, Interorbital septum.||qj, Quadratojugal.|
|j, Jugal.||sa, Supra-angular or coronoid.|
|l, Lacrymal.||so, Supra-occipital.|
|mx, Maxillar.||sq, Squamosal.|
|n, Nasal.||ty, Tympanic cavity.|
|os, Orbito-sphenoid.||v, Vomer.|
|p, Parietal.||1, Exit of olfactory nerve.|
The Hyoid apparatus is, in its detail, subject to many variations in accord with the very diverse uses to which the tongue of birds is