Vertebrate Skeleton
Biology SSS 1 Second Term
WEEK 2
Vertebrate Skeleton
Performance Objectives
Student should be able to:
- Explain the axial
- Explain appendicular skeleton
Content
The mammalian skeleton is made up of the axial and appendicular skeleton.
Axial Skeleton
The axial skeleton is made up of the skull, vertebral column or backbone, the ribs and sternum or breastbone.
The Skull
The skull is composed of the cranium (brain box) and facial bones. The cranium consists of several flat bones joined together by saw-like edges called sutures. The facial bones support the nose, the eyes and the muscle of the cheeks. Jawbones consist of the upper jaw known as the maxilla and the lower jay known as mandible.
Vertebral column
The vertebral column is also known as the backbone or spinal column. It is the central supporting structure of the skeleton. The vertebral column forms the backbone of the vertebrate animals and protects the spinal cord. It is made up of five groups of bones called the vertebrae (singular, vertebra) in mammals. In humans, it consists of 33 vertebrae. The vertebrae are held one to the others with strong ligaments having compressible cartilage pads called intervertebral discs between consecutive vertebrae.
In mammals, the five different vertebrae are:
- Cervical vertebrae - found in the neck region
- Thoracic vertebrae - found in the chest region
- Lumber vertebrae - found in the upper abdomen
- Sacral vertebrae - found in the lower abdomen
- Caudal vertebrae - found in the tail region
Appendicular Skeleton
The appendicular skeleton is made up of the limb girdles (pectoral and pelvic girdles) and the limbs (forelimbs and hind limbs).
The Limbs
The limbs are made up of the forelimbs (bones of the hands) and the hind limbs (bones of the legs). The limbs of most vertebrates are built on the same basic plan i.e. pentadactyl limb plan (5-digit plan). It is made up of a long bone followed by a pair of two long bones which lie side by side.
The pair of these long bones is followed by a set of nine small bones which are arranged in three rows. The nine small bones are followed by five digits. Each digit is made up of small bones called phalanges.
Sternum
The sternum is the bone that lies in the anterior midline of the thorax. It forms part of the rib cage and the anterior-most part of the thorax. Its functions are to protect the thoracic organs from trauma and also from the bony attachment for various muscles. It is also the centre around which the superior ten ribs directly or indirectly attached.
The sternum is also known as the breastbone. It is a flat bone that articulates with the clavicle and the costal cartilages of the upper seventh ribs (true ribs), while the eighth, ninth and tenth ribs (false ribs) are indirectly attached with sternum via coastal cartilage of the ribs above.
The Ribs
The ribs are long semi-circular rods connecting the thoracic vertebrae to the breastbone (Sternum). It is found in the chest region of mammals. There are twelve pairs of ribs in humans and thirteen pairs in rabbit. The bony cage formed by ribs protects the lungs and heart. It also assists in breathing.
A typical rib consists of a head (which fits between successive thoracic vertebrae), a neck and the main part, the shaft. Each rib articulates with the thoracic vertebrae by two processes: the capitulum which articulates with facets of the centre of two nearby vertebrae and the tuberculum (tubercle) which articulates with a transverse process.
The first seven pairs of ribs are called the true ribs because they are connected directly with the sternum in front (ventrally) costal cartilages. The next five pairs of ribs are called false ribs because the eighth, ninth and tenth pair of ribs have a common connection with the sternum, each being attached to the costal cartilage of the rib above. The eleventh and twelfth pair are called floating ribs because they have no connection whatsoever with the sternum.