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VERTEBRATE LIFE AND ORGANIZATION 



Figure 21.5. Girdles of the frog. A, A ventral view of the sternum and pectoral 

 girdle; B, a lateral view of the pelvic girdle. (Modified after Gaupp.) 



transverse process represents a true vertebral process fused with a short, 

 rudimentary rib. Free ribs articulating movably with the vertebrae are 

 absent in the adults of all but a few very primitive species of frogs. 

 Foramina for the passage of the spinal nerves are found laterally between 

 successive vertebrae. 



The most anterior vertebra, known as the atlas, is modified for 

 articulating with the skull and lacks transverse processes. The vertebra 

 preceding the urostyle, the sacral vertebra, is also modified with unusu- 

 ally large transverse processes, for supporting the pelvic girdle. 



Appendicular Skeleton. The sternimi, though a part of the axial 

 skeleton, is intimately associated with the pectoral girdle. Sternum and 

 girdle together form an arch of bone and cartilage that nearly encircles 

 the front of the trunk and supports the pectoral appendages. Each half 

 of the pectoral girdle (Fig. 21.5) consists of two bones extending lat- 

 erally from the midventral line, an anterior clavicle and a posterior 

 coracoid. Clavicle and coracoid of opposite sides are connected by a 

 narrow strip of cartilage. Another bone, the scapula, extends dorsally 

 from the lateral end of these. The concavity where these three meet, 

 known as the glenoid fossa, articulates with the humerus, the bone of 

 the upper arm. A partly ossified suprascapula lies dorsal to the scapula 

 and folds over the back of the animal. Only muscles bind the pectoral 



