SCYLLIUM CANICULA 



237 



enters the cranium by a foramen whose position we have already 

 seen. The third vessel/ the common or dorsal carotid artery, takes 

 its origin from the dorsal end of the first efferent loop right beside 

 the first epibranchial artery. It curves forwards and inwards in 

 the sub-mucosa of the roof of the pharynx to a point about level 

 with the spiracle. Here it receives an anastomosing trunk from the 



E.C. 



FIG. 76. Diagram of efferent branchial arteries of Scy Ilium, seen from the 

 ventral side with the left half of the lower jaw and floor of mouth 

 stretched out and the right half cut off. 



A.A., anterior prolongation of aorta; C.C., common carotid ; D. A., dorsal aorta ; E., epibran- 

 chial artery ; E.B., efferent branchial ; B.C., external carotid ; G.C., gill cleft ; H., hyoidean 

 artery: H.M., hyomandibular cartilage; I.C., internal carotid; M., mandibular artery; S.C., 

 sub-clavian ; Sp., spiracle. 



dorsal aorta ; the aorta itself passes forward from the union of the 

 first pair of epibranchials as a small trunk which bifurcates at the 

 level of the first gill cleft, its two ends bending outwards to run into 

 the common carotids. Immediately beyond this the common carotid 

 divides into two, a slender internal or posterior carotid artery and a 

 stouter external carotid.* The former trunk passes inwards to the 



* The naming of these anterior arteries, particularly the carotids, is not 

 satisfactory, as their homologies with the arteries of the higher animals have 

 not yet been accurately determined. 



