30 THE VASCULAR SYSTEM OF THE FEOG 



Dissect as for the veins. Pass a roll of paper or plugs of 

 cotton-wool down the (esophagus, so as to distend it a/nd stretch 

 the aortic a/rches. Gleam carefully the aortic arches, commencing 

 at the trwncus arteriosus ; a^ follow the several arteries to their 

 distribution, removivig the veins a/nd other structures which over- 

 lie them. Rote the division of the trunaus arteriosus in front 

 into right and left branches, each of which again divides into 

 three aortic arches — the carotid arch, the systemic arch, amd the 

 pulmo-cutMiei^asarch. •«**T«'*^w ^.«>.«f)U. 



I. The Carotid Arch is the most anterior of the three arches : 

 it runs round the side of the oesophagus, and is connected 

 dorsally with the second or systemic arch ; its chief branches 

 are as follows : 



1. The lingual artery is a small artery supplying the 



tongue. Immediately beyond the origin of the lingual 

 artery the carotid arch presents a small spongy 

 swelling, the carotid gland. 



2. The carotid artery runs round the side of the cesopha- 



gus to its dorsal surface : it is connected with the 

 systemic arch by a short branch, the ductus BotaUi, 

 which in the adult frog is usually impervious; and 

 then turns forwards beneath the base of the skull, 

 dividing in front into the two following vessels : 

 i. The external carotid artery, supplying the roof and 



sides of the buccal cavity, and the orbit, 

 ii. The internal carotid artery, which entei's the skull 

 and supplies the brain. 



II. The Systemic Arch, the middle arch of the three, runs 

 somewhat obliquely round the ossophagus 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 level of the posterior ends of the kidneys the aorta divides 

 into the two iliac arteries. The branches of the systemic arch 

 are as follows : 



a. Branches given off before the union of the two arches. 



1. The laryngeal artery is a small branch arising from the 



inner side of the systemic arch near its origin from 

 the truncus arteriosus, and svipplying the larynx. 



2. The oesophageal arteries are one or two branches arising 



