653 
serial sections were employed. In experimenting with injecting media 
black India ink was found to give the best results — a method re- 
commended by Mar in the injecting of vascular system of embryos. 
For stages younger than six days, while the heart was still beating, 
the injecting mass was introduced into the liver by means of a very 
fine hypodermic syringe and carried through the circulation of the 
body. For stages six days and older the needle was thrust directly 
into the ventricle. When entirely successful the black vessels formed 
a striking contrast to the white tissue and thus greatly facilitated dis- 
section. 
Fig. 1 represents a camera sketch of the aortic arches and carotid 
arteries of the left side of a chick embryo incubated four and one- 
half days. This specimen was injected through the liver with black 
India ink and, subsequently, dissected so as to expose the arteries of 
the neck region. The left auricle was removed in order to facilitate 
the dissection of the ventral carotid (car. v). 
Fig. 1. Camera sketch of the 
exposed injected arterial system of the 
left side of a chick embryo incubated 
four and one-half days, showing the * Be, chon cio 
exclusive blood supply to the upper 
and lower jaw to be from the ventral 
earotid. >< about 16 diameters. 
Reference letters for all figures: 
a. 1—a.6 aortic arches. art. au. auri- 
eular artery. at. coll. arteria colli col- ; j SS! 
lateralis. e.c. common carotid. car. d. 
dorsal carotid. car. ex. external carotid. : 
ear. in. internal carotid. car.v. ventral carotid. cer.a. cervical artery. in.a. in- 
nominate artery. inf.orb. infra-orbitalis. md. mandibular. ocp.a. occipital artery. 
pl. a. pulmonary artery. s.a. segmental artery. s.car.d. spur from dorsal carotid. 
scl.a. subelavian artery. su.orb. supra-orbitalis. thy. thyroid body. ver.a. vertebral 
artery. x. portion of upper jaw branch of ventral carotid that atrophies. 
Three aortic arches are present, 3, 4 and 6, with their dorsal 
connection still intact. Arches No. 3 and 4 are about the same dia- 
meter and both are slightly wider than the sixth arch. Arising from 
this latter arch (a. 6.), on a level with the ventral carotid (car. v.), is 
the pulmonary artery (pl. a.), which passes to the lung just dorsal to 
the left auricle. 
The third arch (a. 3) gives rise to two vessels, a dorsal (car. d.) 
and a ventral carotid (car. v.). The dorsal carotid, the anterior pro- 
longation of the third arch, is well developed and easily followed as 
it passes forward on the dorsal wall of the pharynx to the brain. 
The first branch to arise from the dorsal carotid is the auricular 
artery (art. au.) which soon after leaving the dorsal vessel divides into 
