pelvic ai(/li(\s almost io the inusculaturo of the l)(»(ly wall 

 siinoundiiig the anus. 



The Carotid Arteries. — The portion of each epi- 

 branchial artery anterior to the entrance of the 1st efferent 

 hianchial 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 

 (^4. Car.^), curves round behind the pharyngo-branchial 

 segment of the 1st 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 

 blanches of the common carotids, the internal carotid 

 arteries (*1. rv//-. ), after perforating the skull at the junction 

 of the prootics and parasphenoid by the carotid foramina 

 (/". car. fig. 2), communicate by a veiy short anastomos- 

 ing vessel {Cir. e.) which completes the eirculus 

 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, lun 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 Yisceral Arteries. — The cadiaco-mesenteric artery 

 (^4. cm.) 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 oesoj)ha- 

 geal artery (^4. os.), which lueaks up on the wall of the 

 (esophagus. It then almost immediately bifurcates, and 



