THE HYPOMERE (LATERAL PLATE MESODERM) 



. Rhombocoel 

 Notochord , 

 ■ Otic vesicle. 

 Dorsal aorta ■ 



Dorsal part 

 aortic arch 



237 



Endocardium 



Myocardium 



Pericardial cavity 



- Pericardium — 



Ventral part of 

 aortic arch 



Larval respiration in the frog. {Top) Development of the external gills. 

 {Bottom) Changes from internal to external gill circulation. 



tend to disappear or become relatively non-functional, as the external 

 gills handle the major volume of the blood flow in this region. 



As the external gills degenerate there develops a short-circuited 

 connection between the afferent (ventral) and the efferent (also ven- 

 tral) ends of the branchial vessels. This probably is aided by the 

 remnant of the original aortic arches. This short circuit supplies the 

 newly forming internal gills. All of the blood from the ventral aorta 



