Question

Sternum of bird is prolonged to form a boat-shaped structure called.
A. Keel
B. Rectrices
C. Xiphoid
D. Dagger

Answer 1

Hint: Bird are also called aves which belong to phylum Chordata due to presence of notochord and class aves, theses animal can due to their hollow bones structure which makes them light bodyweight, except few flightless largest bird ostrich, emu, cassowaries and smallest flightless bird known as kiwi.

Complete answer:
> Option A. The Keel or carina is the extended form of sternum bone which is chest bone, that runs along the midline of the sternum and protrudes and perpendicular to the ribs plane. This carina is present in-flight birds while absent in flightless birds, the keel gives an anchor through which birds wing muscle is attached and held for the flight. This keel appeared as a boat-shaped structure.

> Option B. Rectrices: These are the flight feathers which are present on the tail called rectrices which have a primary function like aid in both lift and trust which enable the flight. Flight feather is the symmetrical shaped, long stiff, pennaceous feather on the tail wing of the bird, those feathers present on the wing called as remiges.

> Option C. Xiphoid: Sternum is the mid-region bone of the chest bone, it is made up of cartilage at the time of birth but later it develops into the bone in adulthood. It is located where ribs are attached to the sternum or chest bone in the human

> Option D. Dagger: It is nothing, such kind of structure present in the skeletal system.

Hence, the correct answer is option (A).

Note: Birds have much pneumatic bone with criss-cross struts that provide structural strength. The air pocket is formed by respiratory air sac within semi-hollow bones of the skeleton. Diving birds like penguin and puffin have non-pneumatized bones.