OR OSSEOUS SYSTEM. 89 



cockatoos, but most generally by means of the thin flexible 

 condition of these bones at their line of junction 5 and by 

 this the gape of birds is widened, to take in or seize bulky 

 objects, which their toothless jaws and the form of their 

 hands do not enable them to subdivide. The basilar part of 

 the occipital bone is short, from the shortness of the cranical 

 cavity, as in reptiles, amphibia, and cetacea, and it extends 

 backwards in the form of a single, round, prominent con- 

 dyle, by which greater extent of rotation is afforded to the 

 head on the neck. The body of the sphenoid is lengthened, 

 as in the inferior vertebrata, and the two pterygoid bones 

 still remain permanently detached, extending laterally to the 

 loose tympanic bones (/.) The tympanic element of the 

 temporal bone, or the os quadratum (/,) is here freely move- 

 able, as in fishes, amphibia, and most sauria ; it sends 

 downwards a convex, prominent, articular surface, for the 

 attachment of the lower jaw, and is likewise attached to the 

 long, slender, malar bone (n,) which forms the inferior boun- 

 dary of the orbit, by which attachment it is enabled to push 

 forwards and upwards the superior maxiUary, and thus 

 widen the mouth. The palatine bones are long, large, and 

 detached, leaving a wide fissure between them ; but the in- 

 termaxillaries are anchylosed to each other, and to the 

 superior jaw bones, which are also united to each other. 

 On the anterior part of the orbits, the large lachrymal 

 bones (e 9 ) and the small superciliary bones (d,) are detached, 

 especially in the rapacious birds ; and, notwithstanding the 

 wide openings of the nostrils externally, the turbinated la- 

 minee are small, soft, and cartilaginous ; the olfactory nerves 

 are transmitted through the back part of the large orbits to 

 the nose, there being no perforation for these nerves in the 

 thin cancellated structure of the ethmoid and sphenoid 

 bones separating the orbits, and here filled with air. The 

 diploe of the cranium, which is largely developed in noc- 

 turnal birds, as owls, is filled with air, like the bones of the 

 trunk and of the extremities, which is admitted through the 

 Eustachean tube, and the cavity of the tympanum ; so that 

 it encreases the intensity of sounds and the dimensions of 

 the organs of hearing. No parts of the skeleton vary so 

 much in birds, as the upper and lower jaws, according to 

 the kind of food on which the different species subsist and 



