408 DEVELOPMENT OF OKGANS IN MAMMALIA. [CHAP. 



The ductus Botalli of the fifth arch (known in Man 

 as the ductus arteriosus) of the side on which the 

 pulmonary arteries are formed, may remain {e.g. in Man) 

 as a soUd cord connecting the common stem of the 

 pulmonary aorta with the systemic aorta. 



The diagram, Fig. 137, copied from Rathke, shews 

 at a glance the character of the metamorphosis the 

 arterial arches undergo in Birds and Mammals. 



Fib. 137. 



Diagrams illustrating the Metamorphosis of the Ar- 

 terial Arches in a Bird A. and a Mammal B. 

 (From Mivart after Rathke.) 



A. a. internal carotid ; b. external carotid ; o. common carotid ; 



d. systemic aorta ; e. fourth arch of right side (root of dorsal 

 aorta) ; /. right subclavian ; g. dorsal aorta ; h. left subcla- 

 vian (fourth arch of left side) ; i. pulmonary artery ; k. and 

 I. right and left ductus Botalli of pulmonary arteries. 



B. a. internal carotid ; h. external carotid ; c. common carotid ; 



d. systemic aorta ; e. fourth arch of left side (root of dorsal 

 aorta) ; /. dorsal aorta ; g. left vertebral artery ; h. left sub- 

 clavian artery ; i. right subclavian (fourth arch of right 

 side) ; k. right vertebral ; I. continuation of right subcla- 

 vian ; m. pulmonary artery ; n. ductus Botalli of pulmonary 

 artery. 



