662 
feeds the dorsal wall of the neck and vicinity of base of the wing 
enters the foramen in the transverse processes of the cervical verte- 
bree and divides into a posterior and an anterior branch. The anterior 
branch runs forward and anastomoses with the occipital (ocp. a.) while 
the posterior branch runs back toward the thorax. 
The external (car. ex.) and internal carotid (car. in.) arteries have 
undergone little change except to increase in size — substantially 
they remain as those described in preceeding figure. 
Fig. 7 shows a drawing of the injected arterial system of the 
neck and head region of an adult fowl. A comparison with preceding 
For can en 
" \ 
Fig. 7. Dissection of injected arterial system of the left side of an adult fowl» 
showing the arteries of the neck and head region. Main branches identical with those 
of Fig. 6. Actual size. 
figure will show that there has been no further changes in the de- 
velopment of the carotid except those incident to the increase in size. 
Summary. 
The origin of the external and internal carotid arteries in birds 
has been in doubt. According to RATHKE the external carotid in 
birds arises in the same manner as in mammals; viz., from the ventral 
remnant of the third aortic arch. Mackay claimed, in 1887, that the 
ventral vessel takes no part in the formation of the external carotid. 
He maintained that both external and internal carotid were derived 
from the dorsal vessel. 
The actual course of events shows a very interesting condition. 
Neither RATHKE or MACKAY were correct in the interpretation placed 
on their observations. The branches of the external carotid when 
