ARTERIA INNOMINATA. CAROTID ARTERIES. 243 



their orifices are covered by the semilunar valves, when those 

 valves are pressed against the sides of the artery. These arte- 

 ries have been described in the account of the heart, (see page 

 468, vol. i.) 



The arteries of the head and of the upper extremities pro- 

 ceed from the upper part of the curve in the following man- 

 ner. 



A large trunk, called Arteria Innominata, goes off first. 

 This is more than sixteen lines in length, when it divides into 

 two branches, one of which supplies the right side of the head, 

 and is denominated the Right Carotid : the other proceeds to 

 the right arm, and from its course under the clavicle, is called, 

 at first, the Right Subclavian. Almost in contact with the first 

 trunk, another artery goes off, which proceeds to the left side 

 of the head, and is called the Left Carotid. Very near to this, 

 arises the third artery, which proceeds to the left arm, and is 

 denominated the Left Subclavian. From these great branches 

 originate the arteries, which are spent upon the head and neck 

 and the upper extremities. 



As these arteries arise from the curve of the Aorta, they are 

 situated obliquely with respect to each other. The Arteria 

 Innominata is not only to the right, but it is also anterior to 

 the two others : and the Left Subclavian is posterior, as well 

 as to the left of the Left Carotid and the Arteria Innomi- 

 nata. 



