. Outlines of zoology. egionof gulls and penguins. The cervical vertebrce have small ribs,fused in most cases with the transverse processes. Thethoracic vertebrae tend to fuse; and numerous vertebra (oneto three dorsals, all the lumbars, and some caudals) fuse withthe tivo or three true sacrals. The terminal vertebrce usuallyfuse as a ploughshare bone. In most birds the bones of the brain-case fuse very early,the sutures being obliterated. Only the lower jaw, thequadrate, the columella, and hyoid are always ?novable; but GENERAL CHARACTERS OF BIRDS. 649 the pterygoids usually articulate freely
. Outlines of zoology. egionof gulls and penguins. The cervical vertebrce have small ribs,fused in most cases with the transverse processes. Thethoracic vertebrae tend to fuse; and numerous vertebra (oneto three dorsals, all the lumbars, and some caudals) fuse withthe tivo or three true sacrals. The terminal vertebrce usuallyfuse as a ploughshare bone. In most birds the bones of the brain-case fuse very early,the sutures being obliterated. Only the lower jaw, thequadrate, the columella, and hyoid are always ?novable; but GENERAL CHARACTERS OF BIRDS. 649 the pterygoids usually articulate freely with the basisphenoid,the lachrymals may remain free, and there may be a joint inthe beak at the end of the premaxillce. There is but onecondyle. A membrane bone called the basitemporal coversthe basisphenoid. There is an interorbital septum formedfrom presphenoid and mesethmoid. The otic bones fuse withadjacent bones and with one another about the same modern birds there are no teeth, but the jaws are covered. ,FlG. 354.—Position of organs in a bird.—After Selenka. «., Nostrils ; tr.^ trachea; cr.^ crop ; k., heart; st.^ sternum ; pr.^proventriculus ; g., gizzard; c, cffica ;^., pygostyle ;/&., pelvis;/fe.,kidney; /., lung. by horny sheaths. The premaxillce are large, and form mostof the beak. There is a complete infra-temporal arcadeformed by a delicate jugal and quadratojugal reaching backto the quadrate. The supra-temporal arcade is usuallyincomplete, but in some cases a process of the squamosal joinsa postorbital process of the frontal. The lower jaw consistson each side of five membrane bones and a cartilage bone-r-the articular—which works on the quadrate. Many of theskull bones have a spongy texture, due to cavities filled withair from the nasal dnd Eustachian tubes. 650 BIRDS. There is a well-developed sternum, generally with a keel,with a separate centre of ossification, to which the pectoralmuscles are in part attached. The strong coracoids reachand a
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Keywords: ., bookcentury1900, bookdecade1910, bookidcu3192, booksubjectzoology
