(D) Humans have $12$ pairs of ribs. These are classified based on their attachment to the sternum. The first $7$ pairs of ribs are called 'true ribs'.

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$X = 12, Y = 7 \implies$ True ribs are attached dorsally to the vertebral column and ventrally to the sternum.

(D) Humans have $12$ pairs of ribs. These are classified based on their attachment to the sternum. The first $7$ pairs of ribs are called 'true ribs'. They are attached dorsally to the thoracic vertebrae and ventrally connected to the sternum with the help of hyaline cartilage. Therefore,$X = 12$ and $Y = 7$.

Class 11 Biology Locomotion and Movement Axial skeleton

Medium

Out of $X$ pairs of ribs in humans,only $Y$ pairs are true ribs. Select the option that correctly represents the values of $X$ and $Y$ and provides their explanation.

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A
$X = 12, Y = 5 \implies$ True ribs are attached dorsally to the vertebral column and sternum on the two ends.
B
$X = 24, Y = 2 \implies$ The true ribs are dorsally attached to the vertebral column but are free on the ventral side.
C
$X = 24, Y = 12 \implies$ True ribs are dorsally attached to the vertebral column but are free on the ventral side.
D
$X = 12, Y = 7 \implies$ True ribs are attached dorsally to the vertebral column and ventrally to the sternum.