Strucuture of ribs:
The ribs are curved bars,which movably articulate with the thoracic vertebrae at the back and while with the sternum in front all collectively forming a bony cage,the thoracic basket.These are 12 pairs of ribs.The upper seven pairs of ribs are attached in front directly to the sternum by hyaline cartilage.These are called true rib.The next three pairs of rib costal cartilage attach indirectly to sternum.They are termed false ribs.The lower two pair of ribs are free in front they are known as floating ribs.Tenth rib is also usually floating in Japanese and some other people.
A rib consists of two parts,Vertebral and Sternal. The vertebral part is long and bony.It articulate with the thoracic vertebrae by facets,the capitulum and tuberculum,(Ribs of mammal and birds are bicephalous) in the first nine ribs and by a single facet,the head in the remaining vertebrae.The sternal part is short and cartilaginous.It articulate with the sternum or sternal part of its upper rib.
Human thoracic is wider from side to side then from front to back. This is an adaptation for the up right posture of the body.It help to maintain equilibrium.In birds an uncinate process is present in ribs for muscles attachment.
The ribs serve three important functions-
(i)They protect the heart,large blood vessels and lungs.
(ii)They bear respiratory musclee(external and internal intercostal muscle).
(iii)Lower two pair of ribs protect the kidney.(11thand 11th)
(i) It is bone of chest.
(ii)It is absent in fish,Turtle.
(iii)It is associated with pectoral girdle in amphibia.
(iv) In man it is made up of cervical manubrium (Presternum),mesosternum and xiphoid process(Metasternum).
(v) In male it is nearly 17cm long.
(vi) Manubrium is broad and thick.
(vii)Mesoternum is made up fine sternebrae.
(viii) Metasternum is represented by xiphisternum which is smallest broad and thin.In mammal a cartilaginous plate is attached with xiphisternum known as xiphoid cartilage(hyaline).
Sternummanubrium+5 sternebrae + xiphisternum.
The sternum has two function:
(i)It takes part in the formation of the protective thoracic basket.
(ii) It plays a role in the respiratory mechanism.
It forms the bony frameworks of limbs and their supporting girdles,and includes 126 bones as follows:-
|1. Upper extermities||2. lower extermities|
|(i) Pectoral girdle: Clavical(2) Scapula(2)||(i) Pelvic girdle(2)|
|(ii) Upper limbs(arms) 60||(ii) Lower limbs 60|
The girdle give articulation to the limb bone.There are two types of girdle pectoral girdle (shoulder girdle) and pelvic girdle(Hip girdle).Each girdle is made up of similar right and left halves(os innominate).