Biology LOCOMOTION AND MOVEMENT

Skeletal System

There are two main forms of skeleton :
(a) Exoskeleton
(b) Endoskeleton

Exoskeleton:- This is developed from epidermis.
Example Hairs, Nails, Claws, Hoofs, Horns and feathers, etc. Exoskeleton is ectodermal in origin & non living. Mesodermal exoskeleton occur in fishes scales, crocodiles, turtles. etc.

Endoskeleton :- It is present inside the body & mesodermal in origin. In vertebrate endoskeleton is formed of bone and cartilage. These are living in nature.

Human Skeleton

Skeletal system consist of a framework of bones and few cartilages. This system has a significant role in movement shown by the body. Skeleton is divided into two parts :
(A) Axial skeleton
(B) Appendicular skeleton

(A) Axial skeleton :-
� In rabbit : 132 and in Human : 80 Bones are present in axial skeleton.
� It lies along the longitudinal axis of body. It includes-
(1) Skull
(2) Vertebral column
(3) Ribs
(4) Sternum.

(B) Appendicular Skeleton :
It includes bones of the limbs and girdles.
It is made of : 126 bones in Man and 128 bones in Rabbit.

Man :
late foetal age - 306
at birth - 270
after birth - 206 ( in adult stage )

Rabbit
128 (app) + 132 (ax.) = 260

BONE OF FORE LIMB

Total number of bones in each fore limb : 30
Arm bone : Humerus - 1
Fore arm : Radius and Ulna- 2
Wrist bones : Carpals - 8
Palm : Metacarpals - 5
Digits : Phalanges - 14

THE HUMERUS

Head : It articulates with the glenoid cavity of scapula to form shoulder joint. (Ball and socket joint).
On the proximal end of humerus bone two processes are present called greater and lesser tubercle.

Deltoid ridge (V-shaped) : Elevated rough part on the shaft where deltoid muscle is affached.

Lower end : Articulates laterally with radius & medialy with ulna.

Coronoid fossa : depression just above the anterior aspect of trochlea. It accomodates
the Coronoid process of ulna when elbow is flexed.

Olecranon fossa : It accomodates the olecranon process when Elbow is extended.