_ 654 
two smaller branches supplying respectively the ear and lateral wall 
of neck in a plane horizontal and superficial to the dorsal carotid. 
No other vessel springs from the dorsal carotid until the posterior 
region of the eye is reached. At this stage no trace was found, either 
by means of dissection or sections, of a vessel arising from the dorsal 
carotid feeding the lateral wall of the pharynx. 
The ventral vessel (car. v.), the basal remnant of the first and 
second aortic arches with possibly some secondary changes, arises, as 
in mammals, from the base of the third arch at the same level as 
the pulmonary artery. Running forward on the ventral wall of the 
pharynx, in the region below the ear it gives off a branch to the 
anlage of the lower jaw, then, turning upwards and outwards, another 
branch arises which feeds the anterior region of the hyoid visceral 
arch. Continuing, the main branch turns toward the upper jaw where 
it spreads out over that surface. 
In this stage the sole blood supply to the anlagen of the upper 
and lower jaws comes from the ventral carotid (car. v.) and no trace 
whatsoever is found of a connecting vessel between the dorsal and 
ventral carotid. Such an anastomosis arises at a later stage of 
development. 
The dissection was verified by sections of the same specimen — 
the dissection having been carried out on the left side, and the right 
side being left intact in order to admit of sectioning. The sections 
Fig. 2. Camera drawing of 
dissection of the injected aortic 
arches and carotid arteries of the 
left side of a chick embryo in- 
cubated five and one-half days, 
showing the anastomosing spur 
from the dorsal carotid. The 
segmental arteries and beginning 
vertebral were not described in 
: descriptive part. >< about 16 dia- 
A meters. 
were cut at right angles to the dorsal and ventral carotids and nearly 
parallel to the aortic arches. 
Fig. 2 shows a camera tracing of the injected arterial system of 
the neck region of the left side of a chick embryo of five and half 
days of development. This specimen was prepared and dissected as 
described under the previous specimen. 
At this stage of development the condition of the aortic arches 
is very similar to that described under Fig. 1. The sixth arch (a. 6) 
oll 
