Skeleton - class-VIII

It forms the main axis. It consists of skull - 22 bones vertebral column - 33 vertebrae, sternum - 1 and ribs - 24.

A- The glenoid cavity or glenoid fossa of scapula is a part of the shoulder. It is a shallow, pyriform articular surface, which is located on the lateral angle of the scapula.

• The phalanges are digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges.
•  Hence, Phalanges are present in both hands and foot.
• The mandible is the largest, strongest and lowest bone in the human face. It forms the lower jaw and holds the lower teeth in place. The mandible is the only movable bone of the skull, not counting the ossicles of the middle ear.
• Hence, Mandible is the only movable bone in the skull of the man.
• So, the correct answer is 'Phalanges - Mandible'.

The main characteristic that is associated with birds is their ability to fly. The entire forelimb has been modified to become a wing. The forelimb is not required to support weight but to restrain prey or for locomotion. 

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.

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

The tarsals are the cluster of seven articulating bones in each foot situated between the lower end of tibia and fibula and the metatarsus. These tarsal bones are calcaneus, talus, cuboid, navicular and 3 cuneiform bones. So, the correct answer is '7'.

• The forelimb comprises of humerus, radius, ulna, carpals, metacarpals, and phalanges.
  
• The humerus is the long bone in the upper arm. It is located between the shoulder and the elbow joint. At the shoulder, the humerus connects to the frame of the body via the glenoid fossa of the scapula. Hence humerus is a bone of forelimb.
  
• So, the correct answer is 'Humerus'.
  

The number of phalanges in animals is often expressed as a "phalangeal formula" that indicates the numbers of phalanges in digits. Most land mammals including humans have a 2-3-3-3-3 formula in both the hands and feet which means that the thumb has two phalanges and the other fingers each have three. So the correct answer is '2,3,3,3,3'.

There are two bones in the shank area which are the tibia and fibula. The fibula is smaller and thinner than the tibia. These two bones connect the ankle to the knee and work together to stabilize the ankle and provide support to the muscles of the lower leg. So, the correct answer is 'Tibia-fibula'.

In the human arm, the trochlea of the humerus is the medial portion of the articular surface of the elbow joint which articulates with the trochlear notch or sigmoid notch on the ulna in the forearm. 

• The forelimb comprises of humerus, radius, ulna, carpals, metacarpals, and phalanges.
  
• The humerus is the long bone in the upper arm. It is located between the shoulder and the elbow joint.
• The roughly triangular area on the anterolateral (front-side) surface of the middle of the humerus is called as the deltoid ridge. The deltoid muscle is attached to the deltoid ridge. Hence a deltoid ridge occurs in the humerus.
  
• So, the correct answer is 'Humerus'.

• Each arm 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).
  
• Hence the number of bones present in an arm is '30'.
• So, the correct answer is '30'.

• The forelimb is composed of the humerus, radius and ulna, carpals (wrist bones – 8 in number), metacarpals (palm bones – 5 in number) and phalanges (digits – 14 in number). Hence radius-ulna is bones of the forelimb.
  
• The olecranon process is the near end of the ulna and it forms the pointed portion of the elbow.
• Sigmoid notch is a large depression in the upper extremity of the ulna that fits the trochlea of the humerus (the bone directly above the ulna in the arm) as part of the elbow joint. It is formed by the olecranon and the coronoid process.
• Hence sigmoid notch of the olecranon process is found in radius-ulna.
• So, the correct answer is 'Radius-ulna'.

Trochanter is the bony prominences present toward the near end of the thighbone or femur. The trochanters are the points at which hip and thigh muscles attach. These trochanters usually serves as muscle attachment sites. So, the correct answer is 'Femur'. 

• We move our hands while walking is a natural motion wherein each arm swings with the motion opposite that of the leg.
• Moving arms in an opposing direction with respect to the lower limb reduces the angular momentum of the body which helps in balancing the rotational motion produced during walking.
• Hence we move our hands while walking for balancing.
• So, the correct answer is 'Balancing'.
  

Epiphyseal plate (hyaline cartilage) is formed between diaphysis and epiphysis. This contributes in bone elongation.

• 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 olecranon is the near end of the ulna which forms the pointed portion of the elbow.
• Hence ulceranon process occurs in ulna.
• So, the correct answer is 'Ulna'.
  

• A pectoral girdle or shoulder girdle attach the bones of upper limb to the axial skeleton.
  
• Each pectoral girdle is formed of two halves. Each half of pectoral girdle consists of a scapula and clavicle. 
• Glenoid cavity is a shallow, pyriform articular surface, which is located on the lateral angle of the scapula. It articulates with the humerus to form the shoulder joint. Hence glenoid cavity is associated with scapula and humerus.
• So,the correct answer is 'Both A and B'.

Digital formula is a way of comparing animals by the number of phalanges that they have in each of their digits. It can be used to study phylogeny or to predict how an animal may use its hands and feet. An animal’s phalangeal formula is simply given as a series of numbers. Most land mammals including humans have a 2-3-3-3-3 formula in both the hands(or paws) and feet. Fore limb of frog is 0-2-2-3-3 and hind limb is 2-2-3-4-3.

So, the correct answer is ‘2-2-3-4-3’.

The humerus is the single bone of the upper arm region. It articulates with the radius and ulna bones of the forearm to form the elbow joint. Distally, the humerus becomes flattened. The much smaller lateral epicondyle of the humerus is found on the lateral side of the distal humerus.

 Long bones are longer than they are wide and they are slightly curved for strength.
– A bone that is curved is structurally able to absorb the stress of the body at several points so the stress will be evenly distributed.
– The straight bone would not be able to evenly distribute the weight of the body and the bone would break more easily.
– Long bones are shaped like tubes with rounded ends that are designed to fit into other bones to form joints.
– The ends of long bones are filled with spongy bone; this makes them light but strong.
– Long bones can be found in the thigh, lower leg, toes, arms, forearms and fingers.

(A) Radius-ulna has a sigmoid notch.