657 
the thyroid body, is the ventral carotid (car. v.). It is to be noted in 
this stage that the definitive subelavian and the ventral carotid arise 
independently and do not join in a common stalk as claimed by 
Mackay. In this stage an anastomosis between the dorsal vessel 
(car. d.) and the anterior branches of the ventral vessel (car. v.) has 
become established. 
The dorsal vessel, as in previous specimens, passes forward as a 
broad continuation of the third arch. In the region of the hyoid 
visceral arch, it gives rise to a branch, which, passing anteriorly and 
ventrally, anastomoses with the ventral carotid so that the blood supply 
to the upper and lower jaw is derived now from two sources — 
through the ventral carotid (car. v.), and also through the anastomos- 
ing branch from the dorsal carotid (car. d.). This anastomosing vessel 
soon after leaving the dorsal carotid gives rise to the occipital artery 
(ocp. a.), and then continuing, divides into two rami on the lateral 
wall of the pharynx — an anterior and a posterior one. The posterior 
ramus forms an anastomosis with the ventral carotid so that the 
arteries of the lower jaw receive blood from both the dorsal and 
ventral vessels. The anterior ramus joins the upper jaw branch of 
the ventral carotid, and assists in forming the arteries of the upper 
jaw. Thus, there is established by these anastomosing rami, in this 
stage, a double source of blood supply to the upper and lower jaw 
— namely through the ventral and dorsal carotid arteries. It is to 
be remembered that the two main blood vessels to the upper and 
lower jaw were derived primarily from the ventral vessel (car. v.) and 
that previous to this anastomosis, the sole blood supply was through 
the ventral vessel (car. v.) — a condition altogether different from the 
claim of Mackay in which he states that the common carotid artery 
“constitutes the sole blood supply to the head”. 
After the dorsal carotid (car. d.) gives rise to this anastomosing 
branch it passes forward as the internal carotid artery (car. in.), and 
shortly there springs from it in the region of the ear, the auricular 
artery which divides into two smaller branches, the mandibular (md) 
which supplies the base of the upper and lower jaws, and the supra- 
orbitalis (su. orb.) which feeds the dorsal wall of the eye. 
It is probable that the communicating vessel (=) between the 
upper and lower jaw branches represents a portion of the upper jaw 
branch of the ventral carotid of the earlier stages. In this specimen 
it has begun to atrophy. 
The lower drawing (B) in this figure shows a detail in the 
relations of the vertebral artery in a specimen of the same age. 
Anat. Anz. XXIX. ‚Aufsätze. 42 
