The Vascular System 221 



the common carotids, cm. The distribution of 

 these two vessels is symmetrical, so that only 

 one need be described. While the collateralis colli, 

 as has been said, carry blood chiefly to the tongue 

 and lower jaw, the common carotids supply the 

 cranium and upper jaw. 



Soon after its formation by the division of the 

 primary carotid, the common carotid is joined, as 

 noted above, with the collateralis colli of that side 

 by the connective, x; since the common carotid 

 and its branches all lie dorsal to the collateralis colli 

 and its branches, the connectives x and x 1 extend 

 in a more or less dorso-ventral direction. The two 

 common carotids, almost completely surrounded by 

 bone, in passing cephalad sweep first laterad, then 

 mediad, so that they together form almost a com- 

 plete ellipse, as seen in Fig. 62; there is, however, 

 no apparent connection between them at the an- 

 terior region where they lie so close together. 



A short distance cephalad to the connective x 

 the common carotid is connected laterally, z, with 

 a rather complicated plexus of vessels lying at the 

 base of the skull ; it is through this plexus that the 

 common carotid is connected with the collateralis 

 colli by the second connective, x 1 . 



The short branch z quickly divides into three 

 parts: (i) a small anteriorly directed vessel which 

 may be called the internal carotid, ic, since it enters 

 the skull through the most ventral of the three 

 foramina in the exoccipital, and probably supplies 



