28 THE VASCULAR SYSTEM OF THE FROG. 
I. The Carotid Arch (the third embryonic arch; the two 
anterior ones disappearing in the adult): the most anterior of 
the three persistent arches: it runs round the side of the 
cesophagus, and is connected above with the second or 
systemic arch: its chief branches are— 
1. The lingual artery: a small artery supplying the 
tongue. Immediately beyond the origin of the lingual 
artery there is a small spongy swelling, the carotid 
gland, on the carotid arch. 
2. The carotid artery: runs forward beneath the base of 
the skull, and divides into 
i. The external carotid artery: supplying the roof 
and sides of the buccal cavity, and the orbit. 
ii. The internal carotid artery: which enters the 
skull and supplies the brain. 
II. The Systemic Arch (the fourth embryonic arch): the 
middle arch of the three that persist in the adult. Runs some- 
what obliquely round the cesophagus to the dorsal surface, and 
unites with its fellow of the opposite side about the level of the 
anterior ends of the kidneys to form the dorsal aorta: near the 
posterior ends of the kidneys it again divides into the two 
iliac arteries. Its branches are :— 
a, Branches given off before the union of the two arches : 
1. The laryngeal artery: to the larynx. 
2. The cesophageal arteries: to the cesophagus. 
3. The occipito-vertebral artery: dividing into 
i. The occipital artery: supplying the side of the 
head and jaws. 
ii. The vertebral artery: a large artery which runs 
back alongside of and above the vertebral column, 
and gives off branches to the muscles of the body- 
wall and to the spinal cord. . 
4, The subclavian artery: arises from the arch immedi- 
ately behind the occipito-vertebral artery, and supplies 
the shoulder and fore-limb, 
