VERTEBRATES. 



295 



that of hyomandibular. There is much evidence tending 

 to show that the lower jaw and the pterygo quadrate bar 



FIG. 105. Skull of cod. (After Hertwig.) The dotted portion is the pterygo- 

 quadrate arch and is equivalent of the upper jaw of the shark (Fig. 104). 



FIG. 106. Diagram (after Wiedersheim) showing the relation of permanent 

 structures (dark) to the gill-arches of the embryo (dotted), h, hyoid arch; 

 I, cartilages of larynx; I, II, III, gill-bars. At the front of h and I is shown 

 in black the hyoid bone of the adult, with its two horns; behind the ear, at 

 the other end of the hyoid arch, is (black) a piece (styloid process) which 

 joins the skull. 



are but modified gill-bars. With the disappearance of 

 gills in the higher vertebrates the branchial arches tend 



