THE VASCULAR SYSTEM. ‘ 135 
and the muscles of the innominate region. The caudal 
artery is the continuation of the aorta beyond the origin of 
the internal iliacs. It extends into the tail (Fig. 72). 
ARTERIES OF THE HEAD AND NECK. 
From the arch of the aorta arise the innominate and 
left subclavian, which supply the sternum, neck, head, and 
anterior extremities with blood. The innominate gives off 
the left carotid and then divides into the right carotid 
and right subclavian (Fig. 73). Sometimes the two caro- 
tids arise as a single trunk from the innominate, which is 
then continued as the right subclavian. In this case the 
common trunk of the carotid usually bifurcates within one 
or two centimeters of its origin, forming the right common 
carotid and the left common carotid, lying on the respective 
sides of the trachea beneath the sternomastoid and the 
sternohyoid muscles. The vagus or tenth cranial nerve and 
the sympathetic trunk lie in the same sheath with the caro- 
tid (Fig. 66). 
Each carotid artery in the neck region gives off the fol- 
lowing branches: a thyroid to the thyroid cartilage and 
gland, and a muscular to the muscles of the neck. At the 
base of the skull, about the middle of the bulla of the tem- 
poral bone, a slight enlargement of the vessel is seen, from 
which arises the very small internal carotid, leading through 
the foramen lacerum medius to the base of the brain, where 
it joins the circle of Willis. The continuation of the com- 
mon carotid is now known as the external carotid. This, 
after giving off a lingual branch to the tongue, an external 
maxillary branch to the lower jaw, a post-auricular branch, 
and a temporal branch, turns to pass along the medial 
aspect of the mandible, where it is named the internal 
maxillary, whose main branches are the inferior alveolar, 
the middle meningeal supplying the dura mater, several 
