ARTERIES 020 



epibranchial artery, arises the root of the carotid artery. This is 

 often called the ' common carotid artery ', but it does not 

 correspond to the vessel of that name in the higher vertebrates. 

 It runs forwards and inwards under the skull and is presently 

 joined by a small branch from the dorsal aorta (see below), after 

 which it becomes the carotid (internal carotid) artery. Behind 

 the orbit it gives off forward an orbital branch which immediately 

 passes through the opening in the floor of the skull and runs 

 forwards along the floor of the orbit to supply the upper 

 jaw and the snout. (This branch is often called the external 

 carotid artery but does not correspond to the external carotid 

 (lingual) of the frog.) The carotid artery continues its course in 

 the carotid groove, towards the middle line, where it unites 

 with its fellow for a short distance, but separates again, passing 

 through the internal carotid foramen into the cranium to supply 

 the brain. Outside the carotid root yet another artery arises 

 from the first efferent branchial vessel. This is the spiracular 

 or hyoidean artery, which starts in a line with the horizontal 

 vessels that join the loops, runs forwards to the spiracle, where 

 it supplies the pseudobranch, crosses the orbital floor, enters the 

 cranium by a small foramen in the inner wall of the orbit, and 

 joins the internal carotid artery. The dorsal aorta ends in front 

 by breaking into two small prolongations that curve outwards 

 and join the carotid roots, forming the definitive carotid arteries. 

 Just before the dorsal aorta is joined by the last pair of epi- 

 branchial vessels it gives off a pair of subclavian arteries, which 

 pass backwards and outwards to the fore-fins. Behind the pharynx 

 it runs backwards along the whole length of the body below the 

 backbone, lying, in the tail, in the haemal canal as the caudal 

 artery. Besides paired vessels to the body-wall, it gives off to 

 the viscera several median vessels, known successively as the 

 coeliac (of which the hepatic is a branch), anterior mesenteric 

 (of which the genital is a branch), henogastric, and posterior 

 mesenteric, and to the kidneys several paired renal arteries. 



VEINS 



The sinus venosus (Fig. 250) receives the whole of the blcx)d 

 returning to the heart by a number of very large veins which 

 are called sinuses, though, unlike the sinuses of the cockroach, 



