STERNUM AND RIBS 0F Oryctolagus 11 .pptx

Zoology

1. STERNUM AND RIBS 0F RABBIT * Ribs + Sternum = Thoracic framework *There are 12pairs of ribs,articulated with the 12 thoracic vertebrae. *Each ribs has two parts,shaft and head. *Head articulates with the vertebra,and shaft with the sternum. *Shaft consists of two segments. *A dorsal bony portion,called vertebral or bony rib,and a ventral cartilaginous part,called costal,sternal,or cartilaginous rib. *The first eight pairs of vertebral ribs are dichocephalous or double-headed. *Each of them has a dorsal head,called tuberculum and a ventral one,called capitulum.

2. *Tuberculum articulates with the tubercular facet of the transverse process,and capitulum with the capitular facet of the centrum. *The last four pairs of ribs are monocephalous (single-headed),without tuberculum.Ther *Sternal portions of the first seven pairs of ribs directly articulate with the sternum. *So they are called direct ribs or true ribs. *Remaining ones are generally called false ribs. *Sternal portions of the 8 th and 9 th ribs do not directly articulate with the sternum . *But remain fused with the 7 th sternal rib. *They are only indirectly connected with the sternum. * Therefore,they are called indirect ribs. *The sternal portions of the last three pairs of ribs are free. *They neither reach the sternum nor articulate with other ribs.

3. *So they are called floating ribs. * sternum,or breast bone,is long,narrow and segmented. *Its segments are called sternebrae . *It has three parts,namely 1)pre-sternum or manubrium,formed of sternebra . 2) mesosternum,formed of four or five sternebrae . 3) Metasternum or xiphisternum,formed of single sternebra . *Attached to the xiphisternum is a broad cartilaginous plate,known as xiphoid or xiphisternal cartilage.