THE APPENDICULAR SKELETON

THE APPENDICULAR SKELETON
The appendicular skeleton is made up of the girdles. That is the pectoral and pelvic girdle, as well as the bones of the limbs which

comprises of the fore limbs and hind limbs.
Here let’s look at the structure, formation, and the functions of these groups of skeletal system.

THE PECTORAL GIRDLES

The pectoral girdle is found in the or around the shoulder in man. It is made of two halves which are held by muscles. Each half of the girdle is made of three bones. These bones are

  1. THE SCAPULA OR SHOULDER BLADE.
  2. THE CLAVICLE OR COLLAR BONE
  3. CORACOID

IN MAMMALS, THE SCAPULA AND THE CORACOID ARE FUSED TOGETHER to form what is called SCAPULA CORACOID.
THE SCAPULA IS A FLAT TRIANGULAR BONE.

AT THE APEX IS A HOLLOW OR CAVITY CALLED GLENOID CAVITY INTO WHICH THE HEAD OF THE HUMERUS FITS TO FORM THE SHOULD JOINT.
Above the glenoid cavity is a small hook-shaped bone called coracoid bone.

On the other surface of the scapula, there is a ridge or spine called the scapula spine. It runs down towards the glenoid cavity.
The scapula spine ends with two projections which are acromion and metacromion.
Acromion is shorter than the metacromion but the metacromion is larger.
The clavicle is a small rod bone attached to the ligament joining the sternum to the acromion of the scapula.
The pectoral girdle especially the surface of the scapula, the two processes and the spine are important for the attachment of muscles and ligaments. The pectoral girdle also provides support for the fore limbs.

THE PELVIC GIRDLE

The pelvic girdle is found in the region close to the waist in man. It consists of two halves which are joined to each other ventrally and to the sacrum dorsally. The fusion is called PUBIS SYMPHYSIS.
Each half is called INNOMINATE BONE
Each half is made up of three bones, which are
1. Ilium
2. Ischium
3. Pubis
At the top of it all is the ilium which is the largest and longest of the three bones. At the lower end is the fused bones, ischium and pubis. The ischium and the pubis enclosed an opening or a hole called OBTURATOR FORAMEN.
It is the through this holes that nerves, blood vessels and muscles pass through. So on the other surface of each half of the girdle where the three bones meet, there is a deep hollow or depression called ACETABULUM where the head of the femur of the hind limb fits in to form the hip-joint which is an example of a ball and socket joint

THE LIMBS

What is a limb? Where can the limb be found?
The limbs are made up of the fore limbs which is the bones of the hands and the hind limbs which are the bones of the legs.
The limbs of most vertebrates are built in the same way or process, and this called PENTADACTYL LIMB—5-digit plan.

It is made up of a long bone which is followed by a pair of two long bones that lies side by side. The pair of these long bones is followed by a set of nine small bones which are arranged in three rows.
T5he nine small bones are followed by five digits. Each digits of the small bone is called phalanges. Here is a diagram of the phalanges of man

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THE FORE LIMBS

What are the fore limbs? Where can we find a fore limb?
So fore limbs of a typical mammal is made up of an upper arm bone, which is a long bone called humerus. It has a pound head which fits in

and articulates with the glenoid cavity of the scapula of the pectoral girdle of the shoulder joint.
The lower of the humerus is like hinged pulley like surface called TROCHLEA. At the trochlea, the humerus articulates with the ulna and radius to form the elbow joint.

The humerus is followed by the bones of the fore-arm. The fore-arm bone are the radius and ulna. The radius is a long bone. It lies in front of the ulna and is slightly curved.

The ulna is longer than the radius. The ulna has a cavity called sigmoid cavity. The trochlea fits into this cavity. The ulna also projects backwards to form a projection called OLECRANON PROCESS

The radius/ulna bone is followed by bones of the wrists which are made of nine small bones arranged in three rows. These bones are called CARPALS. In the fore front, the carpals articulates with the radius/ulna and dixtally with the bones of the digits.
The wrist bones are followed by the bones of the digits. The digit bones are five and they are called metacarpals.
In man the metacarpals are called fingers, and they are also refers to as the phalanges.
In man, each digits has three phalanges with the exception of the thumb which has only two. In Rabbits, the phalanges ends in claws

THE HIND LIMBS

The hind limbs of a typical mammal is made up of the thigh bone called the femur. The femur is the largest and strongest bone found in the body. It is rounded at the proximal end to form a head which fits into the acetabulum of the pelvic girdle to form a hip joint.
Very close to the end of the femur, there are three projections called TROCHANTERS. They are very important for the attachment of muscles. At the distal end of the femur, are two rounded heads called CONDYLES. They articulate with the TIBIA bone. In between the two condyles is a pulley-like hoof.

The shank is made up of two bones called TIBIA and FIBULA. The Tibia is longer and stronger than the Fibula. At the end or proximal there are two grooves into which the condyles of the femur fits into.
The fibula is a small bone which lies outside the tibia. In front of this joint is a small round bone called the PATELLA or KNEE-CAP
The ankle is made up of six bones called tarsals. The inner tarsals projects backward to form the heel bone.
The foot of rabbit is made up of four digits called METATARSALS. Each digit is made up of three phalanges.
Most mammals including man has five metatarsals.

THE

RIBS

The ribs of a typical vertebrate are long semi-circular rods connecting the thoracic vertebrae to the breastbone known as the sternum.
It is found in the chest region of mammals. There are twelve of ribs found in humans while the rabbit has thirteen in number. The bony cage formed by the ribs protects vital organs like the lungs and heart.
It also assist in breathing

So a typical rib consists of a head, which fits in between successive thoracic vertebrae, secondly a neck and most importantly the SHAFT.

Each rib articulates with the thoracic vertebrae by two processes.
i.

The CAPITALUM

which articulates with facets of the two near-by vertebrae and
ii.

The TUBERCULUM

known as tubercle articulates with the transverse process.

The first seven pairs of ribs are called the true ribs because they are connected directly with the sternum by costal cartilages. The next five pairs of ribs are called false ribs because the eighth, ninth and the tenth pair have a common connection with the sternum, each being attached to costal cartilages of the ribs above.
The eleventh and twelfth ribs are called FLOATING RIBS because they have connection whatsoever with the sternum

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