646 ARTERIES OF THE AMNIOTA. 



four branchial arteries. The three foremost of these at first 

 supply gills, and in the Perennibranchiate forms continue to do 

 so through life. The fourth does not supply a gill, and very 

 early gives off, as in the Dipnoi, a pulmonary branch. 



The hyoid artery soon sends forward a lingual artery from its 

 ventral end, and is at first continued to the carotid which grows 

 forward from the dorsal part of the first branchial vessel. 



In the Caducibranchiata, where the gills atrophy, the following 

 changes take place. The remnant of the hyoid is continued 

 entirely into the lingual artery. The first branchial is mainly 

 continued into the carotid and other cephalic branches, but a 

 narrow remnant of the trunk, which originally connected it with 

 the dorsal aorta, remains, forming what is known as a ductus 

 Botalli. A rete mirabile on its course is the remnant of the 

 original gill. 



The second and third branchial arches are continued as 

 simple trunks into the dorsal aorta, and the blood from the fourth 

 arch mainly passes to the lungs, but a narrow ductus Botalli still 

 connects this arch with the dorsal aorta. 



In the Anura the same number of arches is present in the 

 embryo as in the Urodela, all four branchial arteries supplying 

 branchiae, but the arrangement of the two posterior trunks is 

 different from that in the Urodela. The third arch becomes at a 

 very early period continued into a pulmonary vessel, a relatively 

 narrow branch connecting it with the second arch. The fourth 

 arch joins the pulmonary branch of the third. At the metamor- 

 phosis the hyoid artery loses its connection with the carotid, and 

 the only part of it which persists is the root of the lingual artery. 

 The first branchial artery ceases to join the dorsal aorta, and 

 forms the root of the carotid : the so-called carotid gland placed 

 on its course is the remnant of the gill supplied by it before the 

 metamorphosis. 



The second artery forms a root of the dorsal aorta. The 

 third, as in all the Amniota, now supplies the lungs, and also 

 sends off a cutaneous branch. The fourth disappears. The 

 connection of the pulmonary artery with both the third and 

 fourth branchial arches in the embryo appears to me clearly to 

 indicate that this artery was primitively derived from the fourth 

 arch as in the Urodela, and that its permanent connection 



