278 AVES. 



the outer side of the internal angular process, fissures arc commonly continuous with the 



This ligament assumes a fibro-cartilaginous anterior palatal fissure, (7, 7, Jig. 126,) but in 



structure at its anterior part : it is attenuated the full grown Struthious and some Gallinaceous 



internally, and is situated between the two birds, the palatine and maxillary bones unite 



bones in the outer part of the capsular ligament, with the vorner and separate the two fissures, 



At the posterior part of the joint a strong thus increasing the bony floor of the nasal 



fibrous band extends from the end of the mas- cavities. External to the rami of the lower 



toid process to the internal angular process of jaw, the malar or zygomatic bones may in ge- 



the lower jaw, so as to restrain the forward neral be seen converging from the tympanic to 



movement of the jaw. the superior maxillary bones, the elongated 



The skull presents fewer varieties of form in triangular space between these bones and the 



birds than in any other class of vertebrate ani- pterygoid and palatine leads directly from below 



maJs. With the exception of a few species, in into the large orbits. 



which the beak assumes what may almost be The two lateral facets present posteriorly the 

 termed a monstrous development, it has the tympanic or auditory cavity, (Q,jig. 128,) ante- 

 form of a pretty regular five-sided pyramid, of rior to which is the tympanic bone, with the 

 which the occiput forms the base, and the an- malar and inferior maxillary bones extending 

 terior extremity of the beak the apex. forwards from its lower extremity. Above the 



The posterior facet or base of the pyramid tympanic bone is the zygomatic process of the 

 is formed by the upper and larger portion of temporal, (d, fig. 128,) arching over it in the 

 the occiput, together with part of the temporal Struthious and Psittaceous birds, as if to effect 

 bones. It is the smallest facet of the head, its normal connection with the malar bone, 

 and is larger in the transverse than the vertical Between the zygomatic and post-orbital pro- 

 diameter. It presents the vertical prominence cesses is the crotaphyte depression, (g,fig. 128,) 

 corresponding to the narrow cerebellum, which always well-marked, but bounded by ridges 

 is separated by a venous foramen and furrow more or less developed in different birds. At 

 (8, fig. 126) from a broad muscular depression the lower part of this depression may be per- 

 on either side ; below these are the large occi- ceived the large foramen common to the supe- 

 pital foramen, (1, fig. 126); the hemispheric rior and inferior maxillary divisions of the trifa- 

 tubercle, which unites the head to the atlas ; cial nerve. Then come the spacious rounded 

 and on either side of this tubercle a smaller orbits, bounded above by the supra-orbital 

 muscular depression, separated by a transverse lamella, behind by the sphenoid and frontal ex- 

 ridge from the larger one above, and per- pansions, which form, at the same time, the an- 

 forated by the pneumogastric and hypoglossal terior walls of the cranium; separated from each 

 nerves ; these depressions are bounded laterally other, but always more or less incompletely, by 

 by the mastoid processes. (10, 10, fig. 126.) the thin sphenoidal and ethmoidal plates, the 



The inferior facet or base of the skull joins deficiencies of which are supplied in the recent 



the posterior and lateral facets almost at a state by aponeurotic membranes, and defended 



right angle. It is bounded anteriorly and at anteriorly by the largely developed lachrymal 



the sides by the lower jaw, which, on account bones and the ethmoidal alae, between which 



of the compressed form and divarication of the there are always present apertures varying in 



rami, scarcely intercepts any part of the view size. The pterygoid and palatine bones, with 



of this very complicated surface. The occipital the styliform malar bone, form a very incom- 



condyle, with the muscular depressions on plete floor of the orbit. 



either side and the mastoid processes, may be Anterior to the orbits the sides of the skull 



considered in some, and more especially in the become gradually narrower to the end of the 



Struthious birds, as forming part of the base of beak ; between the lachrymal and the superior 



the skull. Anterior to the basilar portion of maxillary bones a large triangular or rounded 



the occiput comes the body of the sphenoid, space is left, (\\,fig. 128,) which conducts to 



which in the Struthionida sends outwards and the nasal cavity. A second vacancy occurs, 



forwards two rounded processes (jj, fig. 126) anterior to this, bounded by the nasal, superior 



to abut against the flattened pterygoid bones, maxillary, and intermaxillary bones, forming 



Between the origins of these, and anchylosed the osseous boundary of the wide external 



to the spine of the sphenoid, the vomer extends nostrils. (12, Jigs. 127, 128.) 

 forwards to a distance varying in different birds. The superior surface of the cranium is gene- 



The tympanic bones are seen on either side of rally convex in relation to and indicative 



the body of the sphenoid, and external to these of the development of the brain; it is round- 



the zygomatic processes of the temporal ; the ed posteriorly, where it is generally widest, 



space circumscribed by these bones, with the Here on each side is seen the temporal de- 



mastoid processes behind, forms the expanded pression : the interorbital space in the Gulls, 



external passage of the ear, which is closed in Petrels, Albatrosses, Penguins, and other sea- 



the recent state by the large convex membrana birds, presents also two depressions, scarcely 



tympani, (8, 8, fig. 126.) Anterior to the less marked, of a semilunar form, the convexi- 



tympanic bones the pterygoid processes (i i, ties meeting in the mesial line, and lodging a 



fig. 126) extend forwards and inwards to join gland, whose secretion is carried into the nose 



the palatine bones; which are then continued to lubricate the pituitary membrane. Slight 



forwards to the superior maxillary, leaving traces of these glandular depressions may be 



between them the large posterior nasal fissure seen at 13, fig. 127, in the Ostrich. In other 



divided longitudinally by the vomer. These birds the iiiterorbital space is moderately con- 



