408 DEVELOPMENT OF ORGANS 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 solid 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. 



FIG. 137. 



DIAGRAMS ILLUSTRATING THE METAMORPHOSIS OF THE AR- 

 TERIAL ARCHES IN A BIRD A. AND A MAMMAL B. 



(From Mivart after Kathke.) 



A. a. internal carotid ; b. 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 subcla- 

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

 I. right and left ductus Botalli of pulmonary arteries, 



B; a.' internal carotid ; b. 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) ; Jc. right vertebral ; I. continuation of right subcla- 

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

 artery. 



