Tag: skeleton, joints and muscles

• 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.

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 (forelimb) are humerus, radius and ulna, carpals (wrist bones 8 in number), metacarpals (palm bones 5 in number) and phalanges (digits 14 in number).

The salts of magnesium and calcium forms an integral part of the skeletal system. Magnesium combines with phosphates, to form magnesium phosphate which contributes to the bone density. It forms major part of dry matter of bones. Osteoporosis is caused, due to the decrease in the density of calcium and magnesium salts in the body. It also helps in muscle contraction. 60% of the total magnesium are present in the bones.
So, the correct option is D.

2 muscles namely flexor and extensor are involved in the movement of the bone. This is because a muscle cannot work in 2 directions. It can only pull a bone, but cannot push it. So, option B is the correct answer. 

The human shoulder is made up of three bones: the clavicle also known as collarbone, the scapula also known as shoulder blade, and the humerus.

Cervical = 7
Thoracic = 12
Lumbar = 5
Sacrum = (1) 5
Coccyx = (1) 4
Total No. of bones 33