EMBRYOLOGY 



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vessel in each arch and the two suprabranchial arteries the 

 tadpole, while it differs from the dogfish, resembles certain 

 other fishes (p. 382). When the lungs are formed, a vessel 

 to supply each of them arises from the fourth efferent 

 branchial vessel of the same side. Before the gills are 

 lost, direct communication is established between the 

 afferent and efferent vessels, so that when the gill capillaries 

 disappear blood can pass direct from ventral to dorsal 



dar. 



Fig. 381. — Diagrams showing how the arterial systems of adult verte- 

 brates are related to that of the embryo. 



A, Theoretically complete system of arches, not found in this form in any vertebrate 

 adult or embryonic ; B, the system of the adult frog ; C, that of the adult bird ; 

 D, that of the adult mammal. 



I.-VI.j Visceral arches ; Br.i-Br.4, branchial arches ; c.car., common (dorsal) 

 carotid ; ccel., cceliac ; d.ao., dorsal aorta ; d.ar., ductus arteriosus ; hd., hyoid 

 arch ; Ing., lingual, representing ventral carotid ; md. t mandibular arch ;^«/., 

 pulmonary ; set., subclavian ; thy., small vessel to thyroid, representing ventral 

 carotid of embryo ; tra., small vessel to trachea, representing ventral carotid ; 

 v.ao., ventral aorta ; v.car., ventral carotid. 



aorta through four continuous aortic arches. After the loss 

 of the gill capillaries certain parts of the four arches 

 disappear, while other parts persist and become the great 

 arteries of the adult. The first branchial arch becomes 

 the carotid. The portion of the suprabranchial artery 

 which connected it with the arch behind it is usually 

 obliterated, but sometimes there remains a trace of it 

 known as the ductus Botalli. The second branchial arch 

 becomes the systemic arch. The third branchial arch 



