ENDOSKELETON AND VOLUNTARY MUSCLE 



65 



to the sternum or breast bone. The eleventh and twelfth pairs 

 of ribs are known as floating ribs. In many birds and some 

 reptiles a thoracic rib may bear an uncinate process directed 

 backward and overlapping the rib behind, thus reinforcing the 

 thoracic framework (Fig. 44). 



Fig. 39. — A, sternum of Man showing the manner in which the ribs are 

 attached by costal cartilages, c. e, ensiform process; g, gladiolus or body; M, 

 manubrium. B, view of a thoracic vertebra from the right side with the dorsal 

 end of the corresponding rib rotated so as to show its posterior aspect and the 

 manner in which it articulates with the vertebra, d, diapophysis; h, capitular 

 head of rib; p, parapophysis; t, tubercular head of rib. 



Pectoral Girdle and Sternum. — There is a difference of opinion 

 as to whether the sternum evolved in connection with the 

 anterior limb girdle or from ribs. In the frog the sternum is an 

 integral part of the pectoral girdle, the combined elements form- 

 ing a bony structure almost completely encircling the body at the 

 level of the forelimbs. On each side of the body, the girdle is 



