346 



METAZOAN PHYLA 



The circulation of the dogfish is typical of fishes generally (Fig. 242). 

 The blood passes from the ventricle forward in a ventral aorta and by 

 afferent branchial arteries to a capillary network in the gills, where it is 

 oxygenated and where the carbon dioxide is given off. It is collected 

 again by efferent branchial arteries which carry it to the dorsal aorta, 



Olfactory bulb 



Olfactory tract 



Medulla 



Fig. 243. — Brain of a European dogfish shark, Scyllium canicula Cuvier. Dorsal 

 view. {From a Ziegler model, after Wiedersheim.) The roots of the cranial nerves are 

 marked by roman numerals. 



by which, in turn, it is distributed throughout the body. Returning 

 from the peripheral vessels by the veins the blood is carried back to the 

 heart, that from the tail passing through a renal-yortal system in the 

 kidney, that from the alimentary tract through a hepatic-portal system 

 in the liver. A portal system is a capillary system interposed in the 

 course of a vein. All of the venous blood is received by the sinus venosus, 

 from which it passes into the auricle, or atrium, and then into the ven- 



