Tag: our skeletal system and the skin

The hip joint is a synovial joint formed by the articulation of the rounded head of the femur and the cup-like acetabulum of the pelvis. The cup-like acetabulum forms at the union of three pelvic bones - the ilium, pubis, and ischium. 

Bones provide a supporting structure for the body. It gives a framework to the body that helps in maintaining the shape to the body and they also provide surface so that muscles can be attached. Further. bones act as a lever during locomotion so it is able to turn one axis.
Hence , option  A ( Levers ) is correct.

Pelvic girdle consists of two coxal bones. Each coxal bone is formed by the fusion of three bones ilium, ischium and pubis. At the point of fusion of the above bones is a cup shaped cavity called as acetabulum to which the thigh bone articulates. The two halves of the pelvic girdle meet ventrally to form the pubic symphysis containing fibrous cartilage.

The bones of the limbs along with their girdles constitute the appendicular skeleton. Each limb is made of 30 bones. The bones of the hand (fore limb) are humerus, radius and ulna, carpals (or wrist bones 8 in number), metacarpals (palm bones, 5 in number) and phalanges (digits 14 in number).

In humans, each limb is made of 30 bones. The bones of the legs (hind limb) are femur (thigh bone, the longest bone), tibia and fibula, tarsals (ankle bones 7 in number), metatarsals (5 in number) and phalanges (digits 14 in number). A cup-shaped bone, called as patella covers the knee ventrally (knee cap).

• Most land mammals including humans have a 2-3-3-3-3 digital formula in both the hands (or paws) and feet. 

The bone surface is not smooth but scarred with bumps, holes and ridges. These are surface markings, where muscles, tendons and ligaments attached, blood and lymph vessels and nerves pass. Depression and openings are
(1) Fissure- narrow, cleft like opening between adjacent parts of bone. Example, Supra of orbital fissure.
(2) Foramen- a bigger, round opening. Example, foramen magnum.
(3) Meatus- a relatively narrow tubular canal. Example, external auditory meatus .
(4) Groves and sulcus- are deep furrow on the surface of a bone or other structure. Example, inter-vertebral and radial grooves of humerus.
(5) Fossa- shallow depressed area. Example, mandibular fossa.

The semilunar notch or the trochlear notch as it is commonly referred to is a  greater sigmoid cavity formed by a large depression in the upper extremity of the ulna. This fits the trochlea of the humerus and becomes  a part of the elbow joint. This is formed by the olecranon and the coronoid process. Thus, the correct answer is option C.

In humans, each limb is made of 30 bones. The bones of the hand (forelimb) are humerus, radius and ulna, carpals (wrist bones 8 in number), metacarpals (palm bones 5 in number) and phalanges (digits 14 in number). Olecranon process is the process of the ulna that forms the outer bump of the elbow and fits into the fossa of the humerus when the arm is extended.