THE STRUCTURE OF THE t'ERTEB RATES 331 



sternum at its median end. The clavicle is accessory 

 to the main arch. In the domestic fowl the coracoid 



From Ziltel's " Palaontologie" (after Dollo) 



FIG. 121. Skeleton of Iguanodon, an extinct reptile belonging to the group of 

 Dinosaurs, found fossil in Belgium. The skeleton is much more highly specialized 

 than that of the fish, the shoulder and pelvic girdles being fully developed, sc, 

 scapula; co, coracoid bone; p, pubis; pp, postpubic process; is, ischium; I-V , digits. 



can be seen as a relatively thick bone on each side at- 

 tached to the breastbone, while the united clavicles 

 constitute the wishbone. 



The pelvic girdle consists of homologous parts, except 

 that there is nothing to represent the clavicle. It be- 

 comes firmly attached to the ribs, and is in man a very 

 solid structure, to afford support to the hind limbs. 

 The cavity for the articulation of the thigh bone or 

 femur is much deeper than that for the arm bone, and 

 is called the acetabulum or vinegar cup, because it more 

 or less resembles the vessel used on the table to hold vin- 

 egar in ancient times. The flat portion of the pelvic 

 girdle, corresponding to the scapula, is called the ilium. 



