260 THE VERTEBRATE SKELETON. 



flattened, likewise imperfectly ossified structures, and articu- 

 late at their distal ends with a pair of long divergent xiphi- 

 sternal horns (fig. 46, 5), which arise from the posterior end 

 of the sternum proper. The last pair of sternal ribs are at- 

 tached to the preceding pair, not to the xiphisternal horns. 



The first and second vertebral ribs differ from the others in 

 the fact that the tuberculum forms a fairly long outstanding 

 process. 



Cervical ribs. 



Movable ribs are attached to all the cervical as well as to the 

 thoracic vertebrae. Those borne by the atlas and axis are long, 

 narrow structures attached by a fairly broad base, and tapering 

 gradually. The ribs borne by the third to seventh cervical 

 vertebrae are shaped like a T with a double base, one limb of 

 which, corresponding to the tuberculum (fig. 41, 7), articulates 

 with a short transverse process arising from the neural arch, 

 while the other, corresponding to the capitulum, articulates with 

 a surface on the centrum. The ribs attached to the eighth and 

 ninth cervical vertebrae are intermediate in character between 

 the T-shaped ribs and the ordinary thoracic ribs. The anterior 

 limb of the T is shortened, the posterior one is drawn out, 

 forming the shaft of the rib. The distal portion of the rib of 

 the ninth cervical vertebra is unossified. 



The Sacral ribs have been described in connection with 

 the sacral vertebrae. 



THE STERNUM. 



The sternum of Crocodiles is a very simple structure, con- 

 sisting of a plate of cartilage (fig. 46, 2) lying immediately 

 dorsal to the interclavicle, and drawn out posteriorly into a 

 pair of long xiphisternal horns (fig. 46, 5). 



THE ABDOMINAL SPLINT RIBS. 



Lying superficially to the recti muscles of the ventral body- 

 wall, behind the sternal ribs, are seven or eight series of 



