(A) In humans,there are $12$ pairs of ribs,so $X = 12$.True ribs are the first $7$ pairs of ribs,so $Y = 7$.These ribs are attached dorsally to the th

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$X = 12, Y = 7$; true ribs are attached dorsally to the vertebral column and ventrally to the sternum.

(A) In humans,there are $12$ pairs of ribs,so $X = 12$.True ribs are the first $7$ pairs of ribs,so $Y = 7$.These ribs are attached dorsally to the thoracic vertebrae and ventrally to the sternum with the help of hyaline cartilage.Therefore,the correct option is $A$.

Class 11 Biology Locomotion and Movement Axial skeleton

Medium

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

A
$X = 12, Y = 7$; true ribs are attached dorsally to the vertebral column and ventrally to the sternum.
B
$X = 12, Y = 5$; true ribs are attached to the vertebral column dorsally and to the sternum at both ends.
C
$X = 24, Y = 7$; true ribs are attached to the vertebral column dorsally but are free ventrally.
D
$X = 24, Y = 12$; true ribs are attached to the vertebral column dorsally but are free ventrally.