AVES. 



275 



the cerebrum are lodged, the rest of the brain 

 is contained in the posterior division. The 

 relative proportion of these divisions varies in 

 the different orders; in the Insessore.s and Ac- 

 cipitrcs the anterior superior depression is the 

 largest; in the Rasores, the posterior inferior 

 depression equals, and in some species, ex- 

 ceeds the former in size. The orbits form two 

 slight projections in the anterior fossa of the 

 cranium, which is partially divided longitu- 

 dinally by a ridge corresponding to the inter- 

 space of the cerebral hemispheres. This is 

 developed in the Gallinaceous birds into a 

 thin falciform osseous crest, which is especi- 

 ally remarkable in the Partridge, Turkey, and 

 Capercailzie. It is also well developed in the 

 Parrot tribe. The sella turcica in all birds is 

 a deep round cell, lodging the pituitary gland, 

 as in the Mammalia. 



The foramen magnum (l,Jig- 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, Jig. 126) is situated immediately below 

 the membrana tympani (8, 8,^.126.) There 

 is no fissure analogous to the foramen lacerum 

 medius. 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, Jig. 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. 



The nasal 

 bones (n, n, 

 jig. 127, 128) 

 are a large 

 and elongated 

 pair, extend 

 ing from the 

 inner side of 

 the ant-orbital 

 processes of 

 the frontal to 



Skull of a Parrot. 



the outer side of the ascending processes of the 

 intermaxillary bones, expanding as they ad- 

 vance forwards, and giving off from their outer 



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, ethrnoidal, inter-maxillary, and superior 

 maxillary bones. 



The lachrymal or nngueal bones fo, o, fig. 1 27, 

 128, l,Jig. 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 of that 

 cavity, while in the Owls they do not at all 

 articulate with the frontal bone. They are 

 smallest in the Rasores and Natatores,a.nd 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,jig. 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 Imessores they are not united together in 

 any part of their extent, except in the Gross- 

 beak, (Loxia Coccothraustcs,) 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. 



Thevotner (q,fig. 126) is rapidly an chylosed 

 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,Jlg. 125, r, 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 



T2 



