Axial skeleton Questions in English

(D) The $Sternum$ (also known as the breastbone) is a flat bone located on the mid-ventral line of the thorax. It serves as the attachment point for the ribs and protects the heart and lungs. Therefore,the correct option is $D$.

(A) In humans, the rib cage consists of $12$ pairs of ribs.
These are classified based on their attachment to the sternum:
$1$. True ribs: The first $7$ pairs are called true ribs because they are attached directly to the sternum via hyaline cartilage.
$2$. False ribs: The $8th$, $9th$, and $10th$ pairs are called vertebrochondral (false) ribs as they do not attach directly to the sternum but join the $7th$ rib.
$3$. Floating ribs: The last $2$ pairs ($11th$ and $12th$) are called floating ribs because their anterior ends are not attached to the sternum at all.
Therefore, the number of true ribs is $7$ pairs.

(A) In the provided diagram of the human rib cage:
$P$ points to the flat bone located in the center of the chest,which is the Sternum.
$Q$ points to the vertebrae located in the thoracic region,which are the Thoracic vertebrae.
Therefore,$P$ is the Sternum and $Q$ is the Thoracic vertebra.

(A) The pectoral girdle (shoulder girdle) consists of the clavicle and the scapula.
It serves as the point of attachment for the upper limbs (appendicular skeleton) to the axial skeleton.
Specifically,the clavicle articulates with the manubrium of the sternum (part of the axial skeleton),while the scapula provides the glenoid cavity for the humerus (part of the appendicular skeleton).
Therefore,the pectoral girdle acts as a bridge connecting the appendicular skeleton to the axial skeleton.

(C) The $Sella$ $Turcica$ is a saddle-shaped depression in the body of the $Sphenoid$ bone of the human skull.
It serves as the protective bony seat for the pituitary gland (hypophysis).
Therefore,the correct option is $C$.

(C) The $U$-shaped bone located at the base of the buccal cavity is known as the $Hyoid$ bone.
It is a unique bone because it does not articulate with any other bone in the skeleton.
Although it is anatomically located in the neck region,it is often grouped with the skull bones in the axial skeleton.
Therefore,the correct option is $C$.

(C) The ribs are classified into three types: true ribs, false ribs, and floating ribs.
The first $7$ pairs of ribs are called true ribs because they are attached directly to the sternum.
This attachment is facilitated by $hyaline$ cartilage, which provides flexibility and structural support to the thoracic cage during breathing.
Therefore, the correct option is $C$.

(B) The human vertebral column consists of $33$ vertebrae arranged in a series.
These are categorized into different regions:
$1$. Cervical vertebrae: $7$
$2$. Thoracic vertebrae: $12$
$3$. Lumbar vertebrae: $5$
$4$. Sacral vertebrae: $1$ (fused)
$5$. Coccygeal vertebrae: $1$ (fused)
Therefore,the total number of thoracic vertebrae in humans is $12$.

(D) The Assertion $(A)$ is incorrect because not all $12$ pairs of ribs are bicephalic. Only the first $7$ pairs (true ribs) are typically considered bicephalic in the sense of having two distinct points of attachment to the vertebral column (the head and the tubercle). The last few pairs (floating ribs) lack these two distinct heads.
The Reason $(R)$ is also incorrect because,while many ribs are bicephalic,it is not a universal feature for all $12$ pairs. Therefore,both the Assertion and the Reason are incorrect.

(C) Let us analyze each statement:
$(A)$ The adult human skeleton consists of $206$ bones. This is True.
$(B)$ There are $12$ pairs of ribs in humans,making a total of $24$ ribs. This is True.
$(C)$ The sternum is a flat bone on the ventral midline of the thorax,not the dorsal side. This is False.
$(D)$ All mammals (except a few) have $7$ cervical vertebrae,not $8$. This is False.
$(E)$ Ribs are bicephalic because they have two articulation surfaces on their dorsal end,which articulate with the vertebral column. This is True.
Therefore,statements $A, B,$ and $E$ are True,while $C$ and $D$ are False.

(B) In humans,there are $12$ pairs of ribs.
They are classified based on their attachment to the sternum:
$1.$ True ribs ($1^{\text{st}}$ to $7^{\text{th}}$ pairs): These are attached directly to the sternum by hyaline cartilage.
$2.$ Vertebrochondral (False) ribs ($8^{\text{th}}, 9^{\text{th}}$ and $10^{\text{th}}$ pairs): These do not attach directly to the sternum but join the $7^{\text{th}}$ rib with the help of hyaline cartilage.
$3.$ Floating ribs ($11^{\text{th}}$ and $12^{\text{th}}$ pairs): These are not connected ventrally to the sternum.
Therefore,the $8^{\text{th}}, 9^{\text{th}}$ and $10^{\text{th}}$ pairs are known as vertebrochondral ribs.

(C) In humans,there are $12$ pairs of ribs.
$1.$ The first $7$ pairs are called true ribs because they are attached dorsally to the thoracic vertebrae and ventrally to the sternum with the help of hyaline cartilage.
$2.$ The $8^{\text{th}}$,$9^{\text{th}}$,and $10^{\text{th}}$ pairs of ribs are known as vertebrochondral (false) ribs.
$3.$ These ribs do not articulate directly with the sternum but join the $7^{\text{th}}$ rib with the help of hyaline cartilage.
$4.$ The $11^{\text{th}}$ and $12^{\text{th}}$ pairs are floating ribs as they are not connected ventrally.
Therefore,option $C$ is the correct statement.

(B) Statement-$I$ is incorrect because ribs are thin,flat bones,not thick irregular bones.
Statement-$II$ is incorrect because the $8^{th}$,$9^{th}$,and $10^{th}$ pairs of ribs are called 'vertebrochondral' or 'false' ribs,not 'floating' ribs. The $11^{th}$ and $12^{th}$ pairs are known as floating ribs because they do not connect to the sternum at all.
Therefore,both statements are incorrect.

(A) The thoracic cage is a bony structure that protects the heart and lungs. It is composed of the $12$ pairs of ribs,the $12$ thoracic vertebrae,and the sternum. The diaphragm is a muscular partition that separates the thoracic cavity from the abdominal cavity and is not a structural component of the thoracic cage itself. The pleura is a serous membrane that surrounds the lungs,not a part of the skeletal thoracic cage. However,among the given options,the diaphragm is a muscle,while the pleura is a membrane. In the context of skeletal anatomy,the diaphragm is the most distinct non-skeletal structure listed that does not form the cage. Given the standard options,the diaphragm is the primary answer as it forms the floor of the thoracic cavity rather than the cage itself.

(B) Statement $A$ is incorrect because the human skull is dicondylic,not monocondylic.
Statement $B$ is correct because the joints between adjacent vertebrae are cartilaginous joints (specifically,symphysis joints).
Statement $C$ is correct because all mammals,including humans,have exactly $7$ cervical vertebrae.
Statement $D$ is incorrect because all ribs are bicephalic,meaning they have two articulation surfaces (head and tubercle) for attachment to the vertebrae.
Statement $E$ is correct because the occipital condyles of the skull articulate with the atlas $(C1)$ vertebra to form the atlanto-occipital joint.
Therefore,the correct statements are $B, C,$ and $E$.