THE DOGFISH 23 



vessel by means of which the blood is conveyed to the abdominal 

 cavity and to the hinder part of the body. 1 



Follow the ventral aorta from the conus arteriosus forward, cut- 

 ting away the skin and muscles between the gill arches. Three 

 afferent arteries will be seen to branch off on each side, the anterior 

 and posterior ones of which divide each into two arteries. Follow 

 these five arteries between the gill slits and study their relation 

 to them. 



Exercise 24. Make a semidiagrammatic drawing of the ventral aorta 

 and the afferent arteries, showing their relation to the gill slits 

 and arches. 



We shall now study the efferent branchial arteries, the dorsal 

 aorta, and their main branches. Insert one blade of the scissors 

 in the left corner of the mouth and carry an incision straight back 

 across the gills as far as the pectoral girdle. From the end of this 

 incision carry another across the floor of the pharynx to the oppo- 

 site side of the body. Turn the flap thus formed, which is the 

 entire ventral part of the head, over to the animal's right and pin 

 it there, exposing the cavity of the mouth and pharynx. 



Remove the mucous membrane from the roof of the mouth and 

 pharynx and from the gill arches, being careful not to injure the 

 blood vessels just beneath it. The cartilages forming the skull 

 and gill arches will now come into view. Four pairs of prominent 

 efferent arteries will be seen converging toward the median line, 

 each one lying along the anterior border of a cartilage. Trace 

 each artery forward to its gill slit and observe its two branches, 

 one of which lies along each side of the slit, anastomosing at its 

 lower end. The fifth gill slit receives a branch of the fourth artery. 

 Observe carefully the short arteries which connect the anterior 

 branch of one efferent artery witfr the posterior branch of the one 

 just in front of it. 



iThe ventral aorta and the afferent branchial arteries should be injected 

 through the conus arteriosus. The rest of the arterial system may be injected 

 through the caudal artery, which is the continuation of the dorsal aorta in the 

 tail. Cut off the tail a short distance back of the anus and insert the cannula 

 in this artery. 



