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’ 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’. 
The short branch z quickly divides into three 
parts: (1) 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 
