655 
gives rise to the pulmonary artery (pl. a.), springing from the arch 
at the same level as the ventral carotid (car. v.). 
The dorsal and ventral carotids, arising from the third arch (a. 3), 
have undergone little change in size through they have both increased 
in length owing to the elongation of the neck. The vessels are easily 
followed as they pass forward to the head. There arises from the 
dorsal carotid (car. d.), at a point about midway between the third 
arch and the posterior border of the eye, a new branch (s. car. d.), 
which in later stages anastomoses with the ventral carotid, and ulti- 
mately forms the fork of the external carotid (car. ex.). This branch 
supplies the lateral wall of the pharynx bending out and back toward 
the bifurcation of the ventral carotid into its two main branches, but, 
as yet, no anastomosis has taken place between the dorsal and ventral 
vessel. 
The auricular artery (art. au.) is constant in position and may 
serve as an anatomical landmark. It divides into two branches one 
of which (mandibular) carries blood to the superficial muscles of the 
base of the upper and lower jaw, while the other (supra-orbitalis) 
feeds the dorsal region of the eye. 
In this specimen there were observed two vessels upon the ventral 
carotid not seen in earlier stages. They lie between its bifurcation 
into upper and lower jaw branches and the third arch. One feeds 
the lateral wall of the neck dorsally, and one ventrally to the ventral 
carotid. As in the preceding stage, the main branches to the upper 
and lower jaw are derived exclusively from the ventral vessel (car. v.). 
This and the previous specimen represent interesting stages in the 
development of the carotid when considered from the standpoint of 
the work of Mackay. Mackay claims that the ventral carotid (car. 
v.) has nothing to do with the formation of the external carotid. He 
also says: “It is important to notice at the close of the sixth day 
that, while the third arch is still complete, the common carotid the 
only vessel which passes to the supply of the head is 
prolonged from the dorsal extremity of the arch and occupies a 
position on the front of the ventral bodies close to the middle line 
and to its fellow of the opposite side.” In this he is clearly mistaken, 
and the observation of RATHKE which he was attempting to overthrow 
is much nearer the truth, although it lacks much in showing the true 
condition. 
The point which has been missed so far by observers is, that the 
blood vessels supplying the upper and lower jaw are derived 
primarily from the ventral carotid (car. v), and for a period this 
