422 PROCEEDINGS OF THE ACADEMY OF [May, 



twig, mg, that goes to the musk gland on the side of the mandible 

 and to the skin of that region; (2) a large branch, the mandibular, 

 md, that enters the large foramen on the mesial side of the mandible 

 and extends in the cavity of that bone throughout its entire length; 

 (3) the lingual artery, P, which, in turn, divides, some distance 

 cephalad, into two branches, one extending along the lateral region, 

 the other nearer the mid-ventral surface of the tongue. It is seen, 

 then, that the collateralis colli arteries supply directly the lower side 

 of the head — tongue, mandible etc. — though they may also send 

 blood through the above-mentioned connectives to the brain and 

 dorsal regions of the skull. 



The 'primary carotid, capr, as was noted above, makes a curve to 

 the left after leaving the heart and then passes back to the median 

 plane, where it may be seen lying against the ventral side of the neck 

 muscles and dorsal to the oesophagus; in this place it gives off a 

 series of unpaired cervical arteries, fig. 4, ce, each of which almost 

 immediately divides into an anterior and a posterior branch that 

 carry blood to the cervical vertebrae. At the base of the skull, in 

 the region where it is united by the first connective, x, with the 

 collateralis colli, as described above, the primary carotid divides 

 into two similar branches, called by Bronn 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 lateralad then mediad, so 

 that they together form almost a complete ellipse, as seen in figure 

 4; there is, however, no apparent connection between them at the 

 anterior region Avhere 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 



