Tag: our skeletal system and the skin

There are 7 cervical vertebrae. All cervical vertebrae have apertures in their transverse processes, known as Foramina transversalis, which form vertebro-arterial-canals on either side for vertebral artery to pass through to supply brain and spinal cord.

Looking to the bone, it reveals that the 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. Some of the important depression and openings are 
(1) Fissure- narrow, cleft-like opening between adjacent parts of the bone. Example: Superior orbital fissure.
(2) Foramen- a bigger, round opening. Example: Foramen magnum in the skull. Obturator foramen is a large oval or irregularly triangular aperture in the hip bone (pelvic girdle of mammals), the margins of which are formed by the pubis and the ischium.
(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 the humerus.
(5) Fossa- shallow depressed area. Example: Mandibular fossa.

The ear ossicles are made up of three bones called as malleus, incus, and stapes. They vibrate to conduct the sound waves from the outer ear to inner ear and then to the brain. There are two forms of the skeleton. The axial skeleton includes all the bones along the body axis (lengthwise). Sternum and ribs are a part of the axial skeleton. The appendicular skeleton includes all the bones that form the upper and lower limbs, and the shoulder and pelvic girdles. Clavicle and scapula are the parts of the pectoral girdle.

The glenoid cavity is a part of the shoulder girdle or pectoral girdle. It is a shallow pyriform, articular surface, which is located on the lateral angle of the scapula. The sternum, commonly known as the breastbone, is a long, narrow flat bone that serves as the keystone of the rib cage and stabilizes the thoracic skeleton. The ilium is the uppermost and largest bone of the pelvis and appears in most vertebrates including mammals and birds, but not bony fish. The acetabulum is the socket of the hipbone, into which the head of the femur fits. Thus, option A is correct.

The appendicular skeleton (126 bones) is formed by the pectoral girdles, the upper limbs, the pelvic girdle or pelvis, and the lower limbs. Their functions are to make locomotion possible and to protect the major organs of digestion, excretion and reproduction.

The external or internal framework which provides support to the body is called skeleton. It is of two types exoskeleton and endoskeleton. The lower group and animals possesses only exoskeleton for protection e.g. Cockroach while higher animals possess both e.g. Fish.

• A joint or articulation (or articular surface) is the connection made between bones in the body which link the skeletal system into a functional whole. They are constructed to allow for different degrees and types of movement.
• Ball and socket joint is a type of freely movable joint. For example, shoulder and hip joints.
• Ball and socket are different from the others in the following because ball and socket is a type of joint which is an articulation between two or more bones whereas the clavicle, skull, and femur are individual bones present in the body.
• So, the correct answer is 'Ball and socket'.

The clavicle is the constituent of pectoral griddle or shoulder gridle. It is called as collar bone which serves as a rigid support from which the scapula and free limb suspended. It is an arrangement that keeps the upper limb away from the thorax so that the arm has maximum range of movement. So, the correct answer is 'pectoral gridle'.