ORGANS OF SUPPORT, 



almost indistinguishable from each other, and the sacral 

 vertebrae are more numerous than in all other forms of ver- 

 tebrata. The canal for the spinal chord in the middle of 

 the sacrum, between the two cotyloid cavities, where the 

 nerves of the posterior extremities commence, is very wide, 

 and corresponds with the great inferior enlargement of the 

 spinal chord at that place. In the intervals between the 

 transverse processes of the sacral vertebrae are contained 

 internally on each side the several unequal lobes of the 

 kidneys. The coccygeal vertebrae are moveable and strong 

 in birds, to support the plumage and muscles of this great 

 and flexible organ of motion. They have long transverse 

 processes, and spinous processes both above and below the 

 bodies, and the last of the vertebrae (Fig. 45. g.} has a 

 lengthened, compressed, crescentic form, to increase the ex- 

 tent of its lateral surfaces. 



The lengthened form of the head in birds depends chiefly 

 on the elongation of the jaws, and corresponds with the 

 lengthened form of the neck, and the various manipulations 

 and prehensile uses to which this part is applied. The 

 cranium is short 'and broad, like that of most cetacea ; it is 

 bounded before by very large orbits, separated from each 

 other only by a thin membranous partition, or by a thin 

 plate of the sphenoid bone, and the bones which form it are 

 anchylosed together, so that all traces of the coronal, sagittal, 



lamdoidal, squamous, and other su- 

 tures have here disappeared, as seen 

 in the skull of the golden eagle, falco 

 fulvus (Fig. 47.) The occipital (a,) the 

 parietal (b } ) the frontal (e,) and the 

 temporal bones are for the most part 

 thin, diaphanous, smooth externally and 

 internally, like the surface of the cere- 

 bral hemisphere, and embrace a large 

 lobed cerebellum, large optic lobes, and 

 smooth hemispheres of the brain, 

 which taper forwards to the ethmoid 

 bone. The nasal (/,) and the superior 

 maxillary bones (g 9 ) are moveable on 

 the frontals, sometimes by a distinct 

 articulation, as in the parrots and 



FIG. 47. 



