188 



Aorta. 



/ 



530 a. b. Diagram of the Varieties of the Branches 

 arising from the Transverse Arch by Abnormal 



Ramification. 



The variations in the origins of the vessels arising from the trans- 

 verse arch of the aorta can take place in three different ways : the 

 number of branches either diminishing, or increasing, or there being the 

 normal number but an abnormal ramification. 



The diminution can take place in the following ways: a) two 

 innominate arteries; b) the left carotid is a branch of the 

 innominate ; c) all the branches are united to form a single anterior aorta. 



The augmentation consists in the following varieties: a) the 

 left vertebral artery arises between carotid and left subclavian ; 



b) an Art. tliyrcoidca ima arises between innominate and left carotid; 



c) an internal mammary artery or Art. tliymica arises from the 

 anterior wall of the transverse arch ; d) the innominate is not pre- 

 sent and all branches arise separately. 



The abnormal ramification may take place in two ways : 

 a) both carotids unite to form one innominate; b) the left caro- 

 t i d arises from the innominate, and the left vertebral artery arises alone. 



