24 Cincinnati Society of Natural History. 
GENERAL ARTERIAL SYSTEM. 
The common carotid arteries (right and left) posteriorly ex- 
tend longitudinally along each side above the gills and be- 
side the pharynx. (Figs. XVIII, XIX, XX, Car.) Extern- 
ally, they connect with the efferent branchial arteries; and 
internally, by means of from four to seven short commissural 
vessels (comw) on each side, they communicate with the 
median dorsal aorta. These commissural vessels usually 
arise nearly opposite the fourth or fifth to the eighth or tenth 
pairs of gills. Posteriorly the common carotids are connected 
with the dorsal aorta nearly opposite each other, and a short 
distance behind the last pair of gills. Anteriorly they con- 
tinue forward on each side of the pharynx, giving off numer- 
ous small twigs to this organ. Each carotid also supplies 
the club muscle with several branches. The most posterior 
pair of these branches seem to supply only that portion of 
the muscle connected with the longitudinal refractor fibers. 
The remaining branches supply the circular constrictor por- 
tion. The bratiches to the “club-muscle’”’ run in the sheet 
of connective tissue which connects the muscle to the dorso- 
lateral body wall on each side. 
Just behind the cartilaginous “pharyngeal basket” of the 
branchial skeleton, each common carotid divides into two 
branches, the external and internal carotid arteries. Each 
external carotid passes forward and downward around and 
outside the pharyngeal basket and runs forward along the 
outer margin of the basal plate. Near the junction of the 
posterior with the anterior segments of the basal plate, a 
small branch is given off which passes upward and inward to 
the ligament attaching the dental plate (vamus lingualis). 
This branch supplies the dental plate but apparently not the 
muscles moving it. The main trunk of the external carotid 
then passes forward along the external margin of the basal. 
plate on each side giving off small twigs to the lateral walls 
of the skull. Anteriorly it breaks up into a number of small 
branches, which supply the muscles and integument in the 
tentacular region. 
Each zxternal carotid continues inward and forward just 
above the pharynx. (See Figs. XVIII and XX.) A rela- 
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