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pelvic arches almost to the musculature of the body wall 
surrounding the anus. 
The Carotid Arteries—The portion of each epi- 
branchial artery anterior to the entrance of the Ist efferent 
branchial vessel may be spoken of as the common carotid 
artery. It is a very short trunk which divides into two 
vessels. The outer of these, the external carotid 
(A. Car.*), curves round behind the pharyngo-branchial 
segment of the Ist branchial arch, and runs forward on 
the ventral surface of the skull. Several branches are 
given off which break up on the internal surface of the 
operculum and on the base of the skull. The internal 
branches of the common carotids, the internal carotid 
arteries (A. car.), after perforating the skull at the junction 
of the prootics and parasphenoid by the carotid foramina 
(f. car. fig. 2), communicate by a very short anastomos- 
ing vessel (Cir. c.) which completes the circulus 
cephalicus. From this transverse anastomosing vessel 
three arteries take origin, which run anteriorly in the 
trough of the parasphenoid. The two external vessels, 
which are the internal carotid arteries, run forwards 
towards the nasal region of the skull. The internal 
median vessel divides, and the two vessels so formed run 
forwards in the trough of the parasphenoid, or eye muscle 
canal, accompanying the eye muscles. Each passes out 
with the corresponding optic nerve, and runs forwards 
towards the eye. 
The Visceral Arteries.—The cceliaco-mesenteric artery 
(A. em.) is an unpaired vessel lying entirely to the right 
side of the body. After leaving the right epibranchial 
artery it passes over the external surface of the right 
precaval vein, and gives off a small branch—the cesopha- 
geal artery (4. @.), which breaks up on the wall of the 
cesophagus. It then almost immediately bifurcates, and 
