660 
The branch referred to as the arteria colli collateralis arises on 
the early part of the eight day. It varies in position; in some 
specimens arising as a branch from the common carotid (c. c.) about 
midway between the subclavian (scl. a.) and vertebral (ver. a.) arteries, 
and in others as a branch from the cervical (cer. a.). There is also 
a variation in respect to right and left sides, — in some specimens 
the artery in question springs from the cervical (cer. a.) on one side, 
and from the common carotid (c. c.) on the other. It feeds the crop, 
ventral wall of the oesophagus and thyroid body. In this figure it is 
shown as a branch from the cervical (cer. a.). 
The cervical is smaller than the vertebral and runs along the 
vagus nerve ending in the superficial parts of the skin just posterior 
to the base of the skull. The vertebral passing dorsally enters the 
foramen of the transverse processes of the cervical vertebrae and 
divides into an anterior and a posterior branch. The anterior branch 
passes forward and anastomoses with the occipital artery, while the 
posterior branch passes back toward the thorax. 
The external carotid (car. ex.) has now reached its adult con- 
dition in regard to its main branches. Soon after leaving the common 
carotid it gives rise to the occipital artery (ocp.a.), one branch of 
which anastomoses with the vertebral while another supplies the base 
of the skull. (It is to be noticed that the occipital artery arises as a 
branch from the external carotid and not from the common Carotid as 
Mackay represents in his scheme.) Continuing, the external carotid 
divides into two established branches on the lateral wall of the neck 
which carry blood to the upper and lower jaw respectively. These 
two branches, it is to be remembered, were originally branches of the 
ventral carotid (car. v.). 
The internal carotid (car.in.) at this stage, gives rise to the 
auricular artery (art. au.) which breaks up into three branches — the 
mandibular (md.), which carries blood to the superficial parts of the 
lower jaw, infra-orbitalis (inf. orb.) and supra-orbitalis (sw. orb.). This 
artery is probably analogous to the stapedia artery of mammals but 
unlike it does not anastomose with the external carotid. 
Fig. 6 shows the further changes in the development of the 
carotid arteries of the neck region of the left side of a chick embryo 
incubated about thirteen days. 
The innominate trunk (?n.a.), arising from the systemic arch, 
passing anteriorly and dorsally, soon divides into the common carotid 
(c. c.) and subclavian divisions (scl. a.). From the subclavian near its 
point of union with the common carotid there arises a branch which 
