ji INTRODUCTION. 



parietals from the frontal. All these have anchylosed at a very early 

 period. The first cranial vertebrae at the base of the occipital bone is 

 short. The sphenoid bone and the parts in front which form the face are 

 lengthened, while the pterygoid portions of the former are detached. 

 The basilar part of the occipital bone ends in a single condyle, and its 

 position at the lower margin of the foramen as well as its rotundity 

 afford mobility to the connection of the occipital (A) bone with the 

 slender circular atlas and the vertebral column generally. The neck 

 being composed of numerous bones (K) is rendered flexible, and this 

 enables a bird to preen its feathers both on the upper and lower 

 surface of the body and to sleep with its head turned round and placed 

 under the wing. The face of a bird is moveable upon the rest of the 

 skull, whether articulated as in parrots or not, the thin nasal (F) 

 bones being elastic to a certain extent. The orbits and organs of vision 

 are large, the former being separated only by a thin translucent plate 

 or membrane, while the latter are largely developed in lieu, to a great 

 extent, to the want of the sense of touch. The lower jaw (P) moves 

 freely and widens the gape very sensibly. The palatine bones are 

 much developed in length and breadth, and these have between 

 them a large fissure. The nostrils are very various in position, 

 shape, and size, and the upper and lower jaws are also very variable 

 and suited to their habits. In some the mandibles are compressed 

 and lengthened, and terminate in a hook ; in others they termi- 

 nate in a point as in woodpeckers; others again are broad, sharp- 

 pointed, hooked, rounded and hard, or as in ducks long, flat, spoon- 

 shaped, and toothed ; while birds of prey have a dense horny bill 

 with the edges sharp, strong, and cutting, and the tip hooked. The 

 bill is composed of two pieces corresponding to the jaws of 

 quadrupeds ; the upper portion (a) is called the upper mandible, 

 which is either continued far back on the forehead and there 

 dilated as to form a casque or helmet, or there is a soft naked skin 

 at the base as in rapacious birds, which is the cere (8) ; the 

 lower portion (6) is the lower mandible. At the base of the upper 

 mandible, concealed or not, and of various shapes, are the nostrils 

 (c), while the high medial keel of the bill is the culmen (d) and the 

 corresponding keel of the lower mandible is the gonys (<?). The 

 margins of both mandibles (/), commonly called the commissure, is 



