The foramen magnum (1,fig.126) is formed, as usual, by the union of the four pieces of the occipital bone : its size is considerable, having relation to the mobility of the cranium upon the spine. The foramen lacerum posterius (2, 2, fig. 126) is situated immediately below the membrana tympani (8, 8, fig.126.) There is no fissure analogous to the foramen lacerum medics. The carotid foramina (3, 3, fig. 126) are transversely oblong, and situated on the body of the sphenoid ; the same bone, in the Ostrich, is perforated immediately anterior to the carotid canal by the Eustachian tube, (4, 4.) The posterior palatine foramina are wide spaces, (5, 5,) separated from each other by the vomer (q, fig. 126). Anterior to these, in the base of the skull, are seen the still wider posterior apertures of the nostrils (6, 6). In the inside of the cranium the internal auditory foramina are distinctly seen. The foramen lacerum an terius is divided into several distinct foramina. The optic foramina, on the contrary, are closely approximated, and frequently blended into one. The olfactory nerves escape each by a single foramen, and are continued to the nose either along a deep groove on the upper part of the orbital septum, or, as in the Toucan, pass through a complete osseous canal.
The bones of the face correspond in number and relative position with those of the Mam malia, but differ considerably in their forms and proportions ; they bear most resemblance to the facial bones of the Rodentia. They are always moveably connected with the bones of the cranium, and retain much longer than these their separate condition.
sides a process which curves downwards to join the superior maxillary bone, to which it has erroneously been considered to belong. The nasal bones soon anchylose with the frontal, ethmoidal, inter-maxillary, and superior maxillary bones.
The lachrymal or ungueal bones (o, o, fig.127, 128, lg. 125) are also of considerable propor tionate size. They are more exposed than in mam malia, and are usually moveably articulated by their mesial or anterior edge to a varying number of the bones of the skull. These are commonly the frontal, nasal, and malar bones; but in the ostrich the lachrymal articulate with the palatine bones ; in the Parrot they extend backwards beneath the orbit to the post-orbitals, and thus complete the bony circumference not that cavity, while in the Owls they do not at all articulate with the frontal bone. They are smallest in the Rasores and Natatores,and attain their greatest development in the diurnal Rap tores. In these the separated supra-orbital bones give additional protection to the eye, over which they form, in conjunction with the lachrymal, the projecting arch so characteristic of the physiognomy of the bird of prey.
The palatine bones ( p, p, fig. 126,) are of great proportional size : each is of an elongated, slender, depressed figure, becoming narrower anteriorly, forming the posterior part of the pa latine arch, and completing with the vomer the boundary of the posterior nostrils. In the Rap tores the palatine bones are united together only by a small part of their anterior extre mities. In the Owls the posterior extremities are widely separated from each other. In
the Insessores they are not united together in any part of their extent, except in the Gross beak, ( Loxia Coccothraustes,) at the anterior extremity. In this bird and in the Parrots, the palatine bones have not a horizontal but a ver tical position, contrary to what they are in most other birds. They are least developed in the Rasores.
The vomer (q, fig. 126) is rapidly anchylosed in the Ostrich with the sphenoid, appear ing as a long, moderately compressed, pointed process, extending forward from the spine of the sphenoid in the interval of the palatine bones, and dividing the posterior aperture of the nose into two lateral halves. In most other birds it remains distinct from the spine of the sphenoid, as it is also in the ostrich at a very early period.
The intermaxillary bone (m, fig. 125, r, fig. 126, 127, 128) determines the form, and constitutes the greater part, of the upper man dible. It consequently presents considerable variety in its figure and proportions, and also in its mode of articulation, in different birds ; but in every species it is of considerable size. When completely ossified, which it is at a very early period, the intermaxillary bone consists of three processes which diverge from, or unite to form, the extremity of the upper mandible : the superior mesial process or nasal plate is lamellate, depressed or flattened hori zontally, extends backwards between and above the lower ends of the nasal bones, and becoming The nasal bones (n, n, fig. 127, 128) are a large and elongated pair, extend ing from the inner side of the ant-orbital processes of the frontal to the outer side of the ascending processes of the intermaxillary bones, expanding as they ad vance forwards, and giving off from their outer wedged, as it were, between their upper ends, is articulated in general by an anchylosis to them and the ethmoid bone. This union, however, always allows of a certain elastic or yielding motion to pressure from below. In the Parrots, where the upper mandible is an important in strument in their climbing habits, the nasal plate of the intermaxillary bone is joined to the cra nium by a ligamentous substance (11,fig. 128). The two lateral or mandibular processes (r, r, fig. 127) of the intermaxillary bones diverge and extend backwards, external and superior to the superior maxillary bones ; and, in the Ostrich, they articulate with the anterior extremities of the malar or zygomatic bones. Throughout their whole course the mandibular processes are in close contact with, and soon become an chylosed to the superior maxillary bones. The ossification of the intermaxillary bone obeys the ordinary law of centripetal development. The lateral moieties are still separate in the chick at the conclusion of incubation; and in the duckling they do not anchylose until six weeks after that period. The union commences at the anterior extremity, while at the opposite or cranial end of the nasal process, traces of the original separation may frequently be observed in. the full-grown bird; these are very con spicuous in the Gulls, ( Laridee).