228 THE DOG-FISH 



inch in length, and gives off laterally the five 

 pairs of branchial arteries. 



b. The branchial arteries arise in pairs from the 

 cardiac aorta, and carry the blood from it to the 

 gills. The two hindmost pairs arise close together, 

 or sometimes by a common trunk, immediately 

 in front of the pericardial cavity. The third pair 

 arises about a quarter of an inch further forwards. 

 At its anterior end, about midway between the 

 pericardial cavity and the mouth, the cardiac 

 aorta divides into right and left branches, each of 

 which again divides into the two anterior bran- 

 chial arteries of its side. 



The first or most anterior branchial artery 

 runs along the outer border of the hyoid arch, 

 extending nearly to its dorsal end, and giving off 

 branches to the gill borne by it. 



The four hinder branchial arteries run in a 

 similar manner along the outer bprders of the 

 first four branchial arches, extending almost to 

 their dorsal ends, and giving ofln anterior and 

 posterior branches to the gills borne by these 

 arches. 



2. The efferent branchial vessels. ^ 



The efferent branchial vessels can be readily injected from 

 the caudal artery in the following manner. Cut across the tail 

 about a couple of inches behind the cloaca. Find the caudal 

 artery in the h&mal arches of the vertebral column, lying 

 immediately below the vertebral centra, and dorsal to the 

 caudal vein, which is the only other structure in the hc&mal 

 arch. Inject the caudal artery with plaster of Paris, coloured 

 ivitfa carmine, and carefully strained so as to remove any 

 particles large enough to plug the vessels. 



Insert one of the blades of a strong pair of scissors into the 

 mouth, and cut back horizontally along the left side through 

 the gill arches, as far back as the last gill-slit; from the 

 hinder end of this incision cut transversely across the floor of 



