534 



ARTERIAL ARCHES OF THE AMNIOTA. 



The ductus Botalli of the fifth arch (known in Man as tlie ductus 

 arteriosus) of the side on which the pulmonary arteries are formed, 

 may remain {e.g. in Man) as a solid cord connecting the common 

 stem of the pulmonary aorta with the systemic aorta. 



The main history of the arterial arches in the Amniota has been 

 sufficiently dealt with, and the diagram, fig. 366, copied from Rathke, 

 shews at a glance the character of the metamorphosis these arches 

 undergo in the different types. It merely remains for me to say a 

 few words about the subclavian and vertebral arteries. 



The subclavian arteries in Fishes \isiially spring from the trunks 

 connecting the branchial veins with the dorsal aorta. This origin, 

 which is also found in Amphibia, is typically found in the embryos 

 of the Amniota. In the Lizards this origin persists through life, but 



Fig. 36(5. Diagrams illi-strating thk metamorphosis of the aetehial arches 

 IN A Lizard A, a Snake B, a Bird C and a Mammal D. (From Mivart after Eathke.) 



A. a. internal carotid ; h. externa] carotid ; c. common carotid ; d. ductus Botalli 

 between the third and fourth arches ; e. right aortic trunk ; /. subclavian ; g. dorsal 

 aorta ; h. left aortic trunk ; i. pulmonary artery ; k. rudiment of ductus JBotalli be- 

 tween the pulmonary artery and the system of the dorsal aorta. 



B. a. internal carotid; h. external carotid; c. common carotid; d. right aortic 

 trunk; e. vertebral artery; /. left aortic trunk of dorsal aorta; h. pulmonary artery; 

 i. ductus Botalli of pulmonary artery. 



C. a. internal carotid ; h. external carotid ; c. common carotid ; d. systemic aorta ; 



e. fourth arch of right side (root of dorsal aorta) ; /. right subclavian ; g. dorsal aorta ; 

 h. left subclavian (fourth arch of left side) ; i. pulmonary artery ; k. and I. right and 

 left ductus Botalli of pulmonary arteries. 



D. a. internal carotid; b. external carotid; c. common carotid; d. systemic aorta; 



f. fourth arch of left side (root of dorsal aorta); /'. dorsal aorta; g. left vertebral artery; 

 /(. left subclavian artery ; i. right subclavian (fourth arch of right side) ; k. right 

 vertebral ; /. continuation of right subclavian; m. pulmonary artery; n. ductus Botalli 

 of pulmonary artery. 



