THE PECTORAL ARCH. 



35 



and independent of, both ; but it is never united witli the 

 vertebras by the intermediation of ribs. At first, it consists 

 of one continuous cartilage, on each side of the body, dis- 

 tinguishable only into regions and processes, and affording 

 an articular sui-face to the bones, or cartilages, of the limb. 

 But ossification usually sets up in the cartilage, in such a 

 way, as to give rise to a dorsal bone, called the scapula, or 

 shoulderblade, which meets, in the articular, glenoiclal 

 cavity for the humerus, with a ventral ossification, tenned 

 the coracoid. 



By differences in the mode of ossification of the various 

 parts, and by other changes, that region of the primitively 



Fijr. 12. 



Jt,.cr 

 i.c7-i 



Fig. 12. — Side-view of the pectoral arch and sternum of a Lizard 

 (Iguana tuberculata). — Sc, scapula ; s.sc, supra-scapula ; cr, cora- 

 coid ; gl. glenoidal cavity ; St, sternum ; x.st, xiphisternum ; m.sc, 

 mesoscapula ; p.cr, precoracoid ; m.cr, mesocoracoid ; e.cr, epicora- 

 coid ; cl, clavicle ; i.cl, interclavicle. 



cartnaginous pectoral arch, which lies above the glenoidal 

 cavity, may be tdtimately divided into a scapula and a supra- 

 scapula ; while that which lies on the ventral side may pre- 

 sent not only a coracoid, but a precoracoid and an epi- 

 coracoid. 



In the great majority of the Vertebrata above fishes, the 



