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The anterior cardinal sinuses, which open into the duct 

 of Cuvier opposite the openings of the posterior cardinal 

 sinuses, extend directly above the gill-arches and around 

 each eye (orbital sinus). The glossopharyngeal and vagus 

 nerves traverse the inner wall and floor of each sinus. 

 Behind the orbit each sinus receives a hyoidean sinus which 

 passes downwards, along the outer surface of the hyomandi- 

 bular cartilage, to the floor of the mouth, where it is con- 

 nected with an inferior jugular sinus, which opens into the 

 duct of Cuvier. 



The ducts of Cuvier also receive the two lateral (epigastric) 

 veins from the pelvic region, and are continuous with each 

 end of the transverse sinus venosus, which opens into the 

 auricle, and which has, in its posterior wall, the two openings 

 of the hepatic sinus of the liver. 



Describe the Heart and Ventral Arterial System of Scyllinni. 



The heart (see page 209) within the pericardium, is ventral, 

 between the gills and in front of the pectoral girdle. The 

 impure blood is driven (to the gills) from the ventricle 

 through the contractile conus arteriosus into the ventral 

 aorta, which gives off five afferent branchial arteries on 

 each side. The two posterior pairs of afferent branchials 

 either arise close together, or as branches of a common 

 trunk from each side ; the third pair arise further forwards, 

 and the two front pairs are branches of the two trunks 

 formed by the bifurcation of the ventral aorta at its anterior 

 end (in front of which end is the thyroid gland). 



In the Skate (Raia] the ventral aorta generally gives 

 off a pair of innominate trunks posteriorly and (by bifurca- 

 tion) a pair anteriorly; and these divide respectively into 

 three and two afferent branchials on each side. 



Explain the Course of the Circulation of the Purified Blood 

 from Gills to Body. 



The purified blood returns direct from gills to body by an 

 efferent branchial system of arteries. (To expose these, 

 remove the mucous membrane lining the roof of the mouth.) 

 The efferents form loops round the clefts (first four pairs) ; 

 and a half-loop vessel on the front of each fifth cleft is 

 connected to the loop of each fourth cleft. A hyoidean 

 artery arises from near the middle of the anterior portion 

 of each of the first loops ; and from their dorsal ends the 

 common carotid arteries are given off. Four pairs of main 



