In the Rasorial birds the coronoid process is feebly developed, but the internal and angular processes are of large size. The latter is very remarkable in the great Cock of the woods, ( Tetrao urogallus,) where it extends upwards and backwards in a curved form for the extent of an inch, affording attachment to the power ful muscles required to produce the wide ex pansion of the mandibles necessary to seize the large fir-cones which constitute its food. In the lamellirostral Palmipedes not only are the internal, and the posterior angular processes of large size, but there are also two eminences for muscular attachment on the outer side of each ramus anterior to the articular surface. In the Gulls an oblique ridge is continued from a single eminence similarly situated.
The articular capsule of the lower jaw is strengthened by ligamentous fibres arising from the lower extremity of the tympanic bone, and passing backwards to be inserted into the outer side of the internal angular process. This ligament assumes a fibro-cartilaginous structure at its anterior part : it is attenuated internally, and is situated between the two bones in the outer part of the capsular ligament. At the posterior part of the joint a strong fibrous band extends from the end of the mas toid process to the internal angular process of the lower jaw, so as to restrain the forward movement of the jaw.
The skull presents fewer varieties of form in birds than in any other class of vertebrate ani mals. With the exception of a few species, in which the beak assumes what may almost be termed a monstrous development, it has the form of a pretty regular five-sided pyramid, of which the occiput forms the base, and the an terior extremity of the beak the apex.
The posterior facet or base of the pyramid is formed by the upper and larger portion of the occiput, together with part of the temporal bones. It is the smallest facet of the head, and is larger in the transverse than the vertical diameter. It presents the vertical prominence corresponding to the narrow cerebellum, which is separated by a venous foramen and furrow (8, fig. 126) from a broad muscular depression on either side; below these are the large occi pital foramen, (1, fig. 126); the hemispheric tubercle, which unites the head to the atlas ; and on either side of this tubercle a smaller muscular depression, separated by a transverse ridge from the larger one above, and per forated by the pneumogastric and hypoglossal nerves; these depressions are bounded laterally by the mastoid processes. (10, 10,fig. 126.) The inferior facet or base of the skull joins the posterior and lateral facets almost at a right angle. It is bounded anteriorly and at the sides by the lower jaw, which, on account of the compressed form and divarication of the rami, scarcely intercepts any part of the view of this very complicated surface. The occipital condyle, with the muscular depressions on either side and the mastoid processes, may be considered in some, and more especially in the Struthious birds, as forming part of the base of the skull. Anterior to the basilar portion of the occiput comes the body of the sphenoid, which in the Struthionidee sends outwards and forwards two rounded processes (j j, fig. 126) to abut against the flattened pterygoid bones. Between the origins of these, and anchylosed to the spine of the sphenoid, the vomer extends forwards to a distance varying in different birds. The tympanic bones are seen on either side of the body of the sphenoid, and external to these the zygomatic processes of the temporal ; the space circumscribed by these bones, with the mastoid processes behind, forms the expanded external passage of the ear, which is closed in the recent state by the large convex mcmbrana tympani, (8, 8, fig. 126.) Anterior to the
tympanic bones the pterygoid processes (i Jig. 126) extend forwards and inwards to join the palatine bones; which are then continued forwards to the superior maxillary, leaving between them the large posterior nasal fissure divided longitudinally by the vomer. These fissures are commonly continuous with the anterior palatal fissure, (7, 7, 126,) but in the full grown Struthious and some Gallinaceous birds, the palatine and maxillary bones unite with the vorner and separate the two fissures, thus increasing the bony floor of the nasal cavities. External to the rami of the lower jaw, the malar or zygomatic bones may in ge neral be seen converging from the tympanic to the superior maxillary bones, the elongated triangular space between these bones and the pterygoid and palatine leads directly from below into the large orbits.
The two lateral facets present posteriorly the tympanic or auditory cavity, (8, fig. 128,) ante rior to which is the tympanic bone, with the malar and inferior maxillary bones extending forwards from its lower extremity. Above the tympanic bone is the zygomatic process of the temporal, (d, fig. 128,) arching over it in the Struthious and Psittaceous birds, as if to effect its normal connection with the malar bone. Between the zygomatic and post-orbital pro cesses is the crotaphyte depression, (g,fig.128,) always well-marked, but bounded by ridges more or less developed in different birds. At the lower part of this depression may be per ceived the large foramen common to the supe rior and inferior maxillary divisions of the trifa cial nerve. Then come the spacious rounded orbits, bounded above by the supra-orbital lamella, behind by the sphenoid and frontal ex pansions, which form, at the same time, the an terior walls of the cranium ; separated from each other, but always more or less incompletely, by the thin sphenoidal and ethmoidal plates, the deficiencies of which are supplied in the recent state by aponeurotic membranes, and defended anteriorly by the largely developed lachrymal bones and the ethmoidal alze, between which there are always present apertures varying in size. The pterygoid and palatine bones, with the styliform malar bone, form a very incom plete floor of the orbit.
Anterior to the orbits the sides of the skull become gradually narrower to the end of the beak ; between the lachrymal and the superior maxillary bones a large triangular or rounded space is left, (11,fig. 128,) which conducts to the nasal cavity. A second vacancy occurs, anterior to this, bounded by the nasal, superior maxillary, and intermaxillary bones, forming the osseous boundary of the wide external nostrils. (12, figs. 127, 128.) The superior surface of the cranium is gene rally convex in relation to and indicative of the development of the brain ; it is round ed posteriorly, where it is generally widest. Here on each side is seen the' temporal de pression : the interorbital space in the Gulls, Petrels, Albatrosses, Penguins, and other sea birds, presents also two depressions, scarcely less marked, of a semilunar form, the convexi ties meeting in the mesial line, and lodging a gland, whose secretion is carried into the nose to lubricate the pituitary membrane. Slight traces of these glandular depressions may be seen at 127, in the Ostrich. in other h hinlc tn hitprnrhitril ace ?•?• motleratelv