66 FRANK BLAIR HANSON 



Figures 14 and 15 show the epicoracoid to have a large mid- 

 ventral portion, rounded out anteriorly and posteriorly (com- 

 parable directly with the so-called presternum of the shark and 

 the omosternum and sternum of the Amphibia), while laterally 

 extend two bars, the parts which originally were continuous 

 with the coracoids. Here there is cut off from the coracoids 

 that material which nature will use in all higher classes of verte- 

 brates in the construction of a presternum. And if it be said 

 that this dipnoid fish is not the direct ancestor of the Tetrapoda, 

 it may be replied that every consideration points to the same 

 condition in the direct ancestor, whatever form it was. Both 

 Paterson, in the rat, and the author, in the mouse, found stages 

 in early embryo of these mammals where the clavicles, extend- 

 ing toward the midline, are closely invested with mesenchy- 

 matous bars which unite into a single, median mass, compar- 

 able at once to this epicoracoid in the dipnoid fish and to the 

 'presternum' of Haswell's shark, and actually in the rodents 

 uniting to form the manubrium. 



2. Amphibia 



A similar sternum is found in the Amphibia. As Howes re- 

 marks, "that the Amphibian sternum is for the most part, if 

 not wholly, a derivative of the shoulder-girdle, there can be no 

 longer a question; and although the researches of Goette ('77) 

 leave us in doubt concerning the hypo (post-omosternum) they 

 show that that can be no derivative of the costal apparatus." 



Parker ('91), believing in the diverse origins of the sternum 

 in the Ichthyopsida and Amniota, also describes a dual origin 

 for the sternum in the Amphibia. He says, "a pair of narrow 

 strips are separated off from the posterior borders of the cora- 

 coids," also "a pair of cartilaginous bands appear in the in- 

 scriptiones tendineae of the mm. recti abdominis. From these 

 four elements the sternum is produced." Ruge considers that 

 these cartilaginous bands are to be looked upon as vestigial 

 ribs. The narrow strips are admitted to be from the shoulder- 

 girdle. 



