SKELETON. 



701 



zygapophyses, below the anapophyses the posterior inter- 

 vertebral notches passages through which the spinal nerves 

 pass out, and anteriorly a similar pair of notches. There are 

 twelve or thirteen pairs of ribs which support the wall of the 

 thorax and aid in the mechanism of respiration. The first 

 seven pairs articulate with the breast-bone, the eighth and 

 ninth are connected to the ribs in front, the others are free. 

 Any one of the first seven or more typical ribs consists of 

 two parts, a vertebral portion articulating with a vertebra, an 

 imperfectly ossified sternal portion connecting the end of 



Fr. 



Na 



I'mx. 



FIG. 383. Side view of rabbit's skull. 



/'/tt-r., Premaxilla ; No... nasal; Fr., frontal; Pa., parietal; /ty., 

 squamosal; S.O., supraoccipital ; Per., periotic ; T., tympanic 

 (the reference line points to the bony external auditory meatus, 

 beneath it lies the inflated bulla) ; PO., paroccipital process. 



the vertebral portion with the sternum. Each of the first 

 nine ribs has a double head the capitulum articulating 

 with the centrum of the corresponding vertebra, and partly 

 with that of the one in front, the tubercle articulating with 

 the transverse process of the corresponding vertebra. The 

 posterior ribs have no tubercles, and the capitular articula- 

 tions are restricted to the corresponding vertebrae. 



The sternum is a narrow jointed plate, with a large keeled 

 prsesternum or manubrium, then five segments composing 

 the mesosternum, then a posterior xiphisternum ending in 

 cartilage. 



